IsAnyDialogOpen (MahApps) not working for child windows

[punker76]

Originally reported at punker76#73

Imported from MahApps/MahApps.Metro#3223

IsAnyDialogOpen property is set to false although a child window is shown using the ShowChildWindowAsync by the MahApps.Metro.SimpleChildWindow extension

What steps will reproduce this issue?

var result = await this.ShowChildWindowAsync<bool>(new UserControl { IsModal = false });

// somewhere else in code

if (this.IsAnyDialogOpen == false)
 MessageBox.Show("you shouldn' see this);

Expected outcome

Property should return TRUE if there is a child window shown. Otherwise there should be another property for it.

Environment

• MahApps.Metro 1.6.1
• MahApps.Metro.SimpleChildWindow 1.5
• Windows OS Win10
• Visual Studio 2017
• .NET Framework 4.7