diff --git a/DeviceUpdateThread.cs b/DeviceUpdateThread.cs
index e70bed4..26c6052 100644
--- a/DeviceUpdateThread.cs
+++ b/DeviceUpdateThread.cs
@@ -14,6 +14,8 @@
 // 2026/09/07 - Mike Pullen - Report device status through the shared status palette
 // 2026/09/09 - Mike Pullen - Read the severity colours where they are shown rather than holding them, so a
 //                            scheme changed while running is followed
+// 2026/09/09 - Mike Pullen - Reported the search into the form only once its window exists, as InvokeRequired
+//                            cannot say which thread owns a form that was never shown
 //*********************************************************************************************************************
 using System;
 using System.ComponentModel;
@@ -144,7 +146,7 @@ private static void GetDevicePorts()
         private static void UpdateDeviceList()
         {
             // Check if the parent has been set and not terminating early
-            if ((null != m_Parent) && (false == Terminating))
+            if (ParentIsReady)
             {
                 // Check if invoke is required (should be)
                 if (m_Parent.InvokeRequired)
@@ -165,8 +167,8 @@ private static void UpdateDeviceList()
         /// </summary>
         private static void BackupInfoBox()
         {
-            // Make sure the parent is valid and not terminating early
-            if ((null != m_Parent) && (false == Terminating))
+            // Make sure there is a window to report into
+            if (ParentIsReady)
             {
                 // Get the current status box state through the parent's interface
                 m_Parent.GetStatusBoxState(out m_sStatusBoxText, out m_StatusBoxTextColor, out m_StatusBoxBackColor);
@@ -181,8 +183,8 @@ private static void BackupInfoBox()
         /// <param name="backColor">IN - Background color to set for the info box</param>
         private static void UpdateInfoBox(string sText, Color textColor, Color backColor)
         {
-            // Make sure the parent is valid and not terminating early
-            if ((null != m_Parent) && (false == Terminating))
+            // Make sure there is a window to report into
+            if (ParentIsReady)
             {
                 // Use parent's method which already handles invoke requirements
                 m_Parent.SetStatusBoxState(sText, textColor, backColor);
@@ -197,8 +199,8 @@ private static void UpdateInfoBox(string sText, Color textColor, Color backColor
         /// </summary>
         private static void RestoreInfoBox()
         {
-            // Make sure the parent is valid and not terminating early
-            if ((null != m_Parent) && (false == Terminating))
+            // Make sure there is a window to report into
+            if (ParentIsReady)
             {
                 // Get the message currently displayed in the info box
                 string sCurrentText;
@@ -225,8 +227,8 @@ private static void RestoreInfoBox()
         /// <param name="deviceException">IN - The failure that stopped the search</param>
         private static void ReportDeviceUpdateFailure(Exception deviceException)
         {
-            // Make sure the parent is valid and not terminating early
-            if ((null != m_Parent) && (false == Terminating))
+            // Make sure there is a window to report into
+            if (ParentIsReady)
             {
                 string sMessage = $"{m_sREADING_DEVICES_ERROR} {deviceException.Message}";
                 m_Parent.SetStatusBoxState(sMessage, StatusPalette.ErrorText, StatusPalette.ErrorBackground);
@@ -248,6 +250,20 @@ private static void ReportDeviceUpdateFailure(Exception deviceException)
         /// </summary>
         public static bool Terminating { get => (null != m_Parent) && (GeneratorForm.RngGuiStates.Terminating == m_Parent.State); }
 
+        /// <summary>
+        /// Whether there is a window to report the search into. A parent has to be set, it has to not be
+        /// closing, and its window has to exist: the search runs on a pool thread and reports by calling the
+        /// form, and every one of those calls decides how to marshal itself by asking InvokeRequired.
+        /// A form that has never been shown has no handle, and InvokeRequired on a handleless control
+        /// answers false, which reads as "already on the right thread" - so the search writes the controls
+        /// from the pool thread and races whoever else is using them. Nothing is displaying a form that has
+        /// no window, so there is nothing to report to and the result is dropped rather than forced in.
+        /// </summary>
+        private static bool ParentIsReady
+        {
+            get => ((null != m_Parent) && (false == Terminating) && m_Parent.IsHandleCreated);
+        }
+
         // Synchronizaion objects
         private static object m_Lock = new object();
 
diff --git a/GeneratorForm.cs b/GeneratorForm.cs
index f9fbf7b..319ec84 100644
--- a/GeneratorForm.cs
+++ b/GeneratorForm.cs
@@ -46,6 +46,13 @@ public interface IGeneratorForm : ISynchronizeInvoke
     {
         BindingList<IRNGDevice> DeviceList { set; }
         bool FileBrowseActive { get; set; }
+
+        // Whether the window exists yet. Background work has to ask before reporting into the form, because
+        // InvokeRequired cannot answer for a form that has never been shown: with no window handle there is
+        // no thread to compare against, so it says false, which reads as "already on the right thread" and
+        // is how a pool thread ends up writing controls directly. Form supplies this from Control.
+        bool IsHandleCreated { get; }
+
         bool Running { get; }
         Color StatusBoxBackColor { get; set; }
         string StatusBoxText { get; set; }
@@ -143,22 +150,11 @@ public GeneratorForm(IRNGSessionData sessionData, IRNGDeviceTimer timer)
             m_StatusLabel.BackColor = StatusPalette.NormalBackground;
             m_StatusIndicator.ForeColor = StatusPalette.NormalText;
 
-            // Start the device update thread and trigger an update
-            DeviceUpdateThread.Parent = this;
-            ThreadPool.QueueUserWorkItem(state =>
-            {
-                m_DeviceUpdateComplete.Reset(); // Clear the device update complete flag
-                try
-                {
-                    DeviceUpdateThread.ThreadProc(state);
-                }
-                finally
-                {
-                    // Signal that the device update has finished however it ended, so a failure does not
-                    // leave the close waiting for an update that will never report itself complete
-                    m_DeviceUpdateComplete.Set();
-                }
-            });
+            // The device search is not started here. It reports what it finds by calling this form, and the
+            // form cannot be called until its window exists, so it is started from OnHandleCreated instead.
+            // Starting it here raced the window into being: a search that finished first had nowhere to
+            // report to and its results were dropped, leaving the port list empty until a device was
+            // plugged or unplugged.
 
             // Create the source from the list of device ports
             m_DeviceBindingSource = new BindingSource();
@@ -970,6 +966,30 @@ private void OnDataPointAdded(double fDataPoint, double fCurrentAverage)
             }
         }
 
+        /// <summary>
+        /// Points the device search at this form and runs one, on the thread pool so the window is not held
+        /// while WMI is asked what is attached. Called once the window exists, because that is what the
+        /// search needs in order to report back.
+        /// </summary>
+        private void StartDeviceSearch()
+        {
+            DeviceUpdateThread.Parent = this;
+            ThreadPool.QueueUserWorkItem(state =>
+            {
+                m_DeviceUpdateComplete.Reset(); // Clear the device update complete flag
+                try
+                {
+                    DeviceUpdateThread.ThreadProc(state);
+                }
+                finally
+                {
+                    // Signal that the device update has finished however it ended, so a failure does not
+                    // leave the close waiting for an update that will never report itself complete
+                    m_DeviceUpdateComplete.Set();
+                }
+            });
+        }
+
         /// <summary>
         /// Initializes the thread pool
         /// </summary>
@@ -1325,6 +1345,20 @@ private void ApplyTheme()
             m_ResultHistogramChart.ApplyPalette();
         }
 
+        /// <summary>
+        /// Event handler for the window being created, which is when the device search can first be run
+        /// </summary>
+        /// <param name="e">IN - The event arguments (not used)</param>
+        protected override void OnHandleCreated(EventArgs e)
+        {
+            base.OnHandleCreated(e);
+
+            // The search runs on a pool thread and reports what it finds by calling this form, so it cannot
+            // start until there is a window for it to call. Started from the constructor it raced the window
+            // into being, and a search that got there first had its results dropped.
+            StartDeviceSearch();
+        }
+
         /// <summary>
         /// Event handler for the system colour scheme being changed while the application is running
         /// </summary>
diff --git a/tests/RandomNumberGenerator.Test/DeviceUpdateThread.Test.cs b/tests/RandomNumberGenerator.Test/DeviceUpdateThread.Test.cs
index 60c16ca..7b1782a 100644
--- a/tests/RandomNumberGenerator.Test/DeviceUpdateThread.Test.cs
+++ b/tests/RandomNumberGenerator.Test/DeviceUpdateThread.Test.cs
@@ -132,6 +132,11 @@ public void Parent_SetAndGetProperty_WorksCorrectly()
             // Create mock parent form
             var mockParent = new Mock<IGeneratorForm>();
 
+            // Stand in for a form that has been shown. The search only reports into a form whose window
+            // exists, because it decides how to marshal by asking the form, and a form with no window
+            // cannot answer that question.
+            mockParent.Setup(mock => mock.IsHandleCreated).Returns(true);
+
             //**************************************************************//
             // Act
             //**************************************************************//
@@ -163,6 +168,11 @@ public void Terminating_ParentNotTerminating_ReturnsFalse()
 
             // Create mock parent form with non-terminating state
             var mockParent = new Mock<IGeneratorForm>();
+
+            // Stand in for a form that has been shown. The search only reports into a form whose window
+            // exists, because it decides how to marshal by asking the form, and a form with no window
+            // cannot answer that question.
+            mockParent.Setup(mock => mock.IsHandleCreated).Returns(true);
             mockParent.Setup(mock => mock.State).Returns(GeneratorForm.RngGuiStates.Idle);
 
             // Set the parent
@@ -196,6 +206,11 @@ public void Terminating_ParentTerminating_ReturnsTrue()
 
             // Create mock parent form with terminating state
             var mockParent = new Mock<IGeneratorForm>();
+
+            // Stand in for a form that has been shown. The search only reports into a form whose window
+            // exists, because it decides how to marshal by asking the form, and a form with no window
+            // cannot answer that question.
+            mockParent.Setup(mock => mock.IsHandleCreated).Returns(true);
             mockParent.Setup(mock => mock.State).Returns(GeneratorForm.RngGuiStates.Terminating);
 
             // Set the parent
@@ -258,6 +273,11 @@ public void ThreadProc_ValidParent_UpdatesDeviceListAndManagesStatusBox()
 
             // Create mock parent form
             var mockParent = new Mock<IGeneratorForm>();
+
+            // Stand in for a form that has been shown. The search only reports into a form whose window
+            // exists, because it decides how to marshal by asking the form, and a form with no window
+            // cannot answer that question.
+            mockParent.Setup(mock => mock.IsHandleCreated).Returns(true);
             mockParent.Setup(mock => mock.State).Returns(GeneratorForm.RngGuiStates.Idle);
             mockParent.Setup(mock => mock.InvokeRequired).Returns(true);
             mockParent.Setup(mock => mock.Invoke(It.IsAny<Action>())).Callback<Action>(action => action());
@@ -346,6 +366,11 @@ public void ThreadProc_ParentNoInvokeRequired_UpdatesDirectly()
 
             // Create mock parent form that doesn't require invoke
             var mockParent = new Mock<IGeneratorForm>();
+
+            // Stand in for a form that has been shown. The search only reports into a form whose window
+            // exists, because it decides how to marshal by asking the form, and a form with no window
+            // cannot answer that question.
+            mockParent.Setup(mock => mock.IsHandleCreated).Returns(true);
             mockParent.Setup(mock => mock.State).Returns(GeneratorForm.RngGuiStates.Idle);
             mockParent.Setup(mock => mock.InvokeRequired).Returns(false);
             
@@ -398,6 +423,11 @@ public void ThreadProc_ConcurrentCalls_RespectsSynchronization()
 
             // Create mock parent form
             var mockParent = new Mock<IGeneratorForm>();
+
+            // Stand in for a form that has been shown. The search only reports into a form whose window
+            // exists, because it decides how to marshal by asking the form, and a form with no window
+            // cannot answer that question.
+            mockParent.Setup(mock => mock.IsHandleCreated).Returns(true);
             mockParent.Setup(mock => mock.State).Returns(GeneratorForm.RngGuiStates.Idle);
             mockParent.Setup(mock => mock.InvokeRequired).Returns(false);
             
@@ -491,6 +521,11 @@ public void ThreadProc_InfoBoxUnchanged_RestoresPreviousMessage()
 
             // Create mock parent form
             var mockParent = new Mock<IGeneratorForm>();
+
+            // Stand in for a form that has been shown. The search only reports into a form whose window
+            // exists, because it decides how to marshal by asking the form, and a form with no window
+            // cannot answer that question.
+            mockParent.Setup(mock => mock.IsHandleCreated).Returns(true);
             mockParent.Setup(mock => mock.State).Returns(GeneratorForm.RngGuiStates.Idle);
             mockParent.Setup(mock => mock.InvokeRequired).Returns(false);
 
@@ -550,6 +585,11 @@ public void ThreadProc_InfoBoxChangedDuringUpdate_NewerMessageKept()
 
             // Create mock parent form
             var mockParent = new Mock<IGeneratorForm>();
+
+            // Stand in for a form that has been shown. The search only reports into a form whose window
+            // exists, because it decides how to marshal by asking the form, and a form with no window
+            // cannot answer that question.
+            mockParent.Setup(mock => mock.IsHandleCreated).Returns(true);
             mockParent.Setup(mock => mock.State).Returns(GeneratorForm.RngGuiStates.Idle);
             mockParent.Setup(mock => mock.InvokeRequired).Returns(false);