diff --git a/src/sentence/unicode.rs b/src/sentence/unicode.rs
index d50a9fc..5a785f2 100644
--- a/src/sentence/unicode.rs
+++ b/src/sentence/unicode.rs
@@ -1571,6 +1571,8 @@ pub(crate) fn leftover_keyval_cs_name(tail: &str) -> Option<&'static str> {
         "tcbifexternal",
         "tcbcontinuedraftmode",
         "tcbinterruptdraftmode",
+        "tcbstartdraftmode",
+        "tcbstopdraftmode",
         "tcbposterset",
         "tcbfontsize",
         "tcbEXTERNALIZE",
@@ -1767,6 +1769,8 @@ fn leftover_keyval_kind(name: &str) -> VerbKind {
         | "sarg"
         | "tcbcontinuedraftmode"
         | "tcbinterruptdraftmode"
+        | "tcbstartdraftmode"
+        | "tcbstopdraftmode"
         | "PyLTVerbatimEnv" => VerbKind::Listingcont,
         "setmintedinline"
         | "usemintedstyle"
@@ -3226,7 +3230,11 @@ fn push_segment_preserving_space(dest: &mut String, piece: &str) {
         })
         // `!!a` is one UAX fragment; inventing `!! a` then splitting
         // `!! a` on the next pass is a wrap/SemBr cycle.
-        && !dest.ends_with("!!");
+        && !dest.ends_with("!!")
+        // After protect_inline_tokens, `.`` ` is `.` + leftover backtick
+        // (`dest="…."`, `piece="`\\0PHn\\0"`). Inventing `. `` ` then
+        // wrapping back is a SemBr cycle (ubuntu CI seed).
+        && !(dest.ends_with(['.', '!', '?']) && piece.starts_with('`'));
     if need_space {
         dest.push(' ');
     }
@@ -3707,6 +3715,15 @@ mod tests {
         UnicodeSentenceSplitter::new().split(text)
     }
 
+    #[test]
+    fn period_then_latex_quotes_does_not_invent_space() {
+        assert_eq!(
+            split("^{`}`.`` A0`"),
+            vec!["^{`}`.`` A0`".to_string()],
+            "must not invent space between . and ``"
+        );
+    }
+
     #[test]
     fn single_quote_bang_capital_stays_one_sentence() {
         assert_eq!(
diff --git a/tests/latex_leftover_cmds.rs b/tests/latex_leftover_cmds.rs
index 503db4c..5a4cf11 100644
--- a/tests/latex_leftover_cmds.rs
+++ b/tests/latex_leftover_cmds.rs
@@ -378,6 +378,8 @@ fn leftover_constructors_do_not_join() {
     leftover_cmd_stays_atomic(r"\tcbposterset{colback=red}");
     leftover_cmd_stays_atomic(r"\tcbcontinuedraftmode");
     leftover_cmd_stays_atomic(r"\tcbinterruptdraftmode");
+    leftover_cmd_stays_atomic(r"\tcbstartdraftmode");
+    leftover_cmd_stays_atomic(r"\tcbstopdraftmode");
     leftover_cmd_stays_atomic(r"\tcbfontsize{2}");
     leftover_cmd_stays_atomic(r"\tcbindex");
     leftover_cmd_stays_atomic(r"\tcbEXTERNALIZE");
@@ -410,6 +412,8 @@ fn leftover_constructors_do_not_join() {
     extras_skip_no_brace("cs");
     extras_skip_no_brace("OptionalLocalPitonStyle");
     extras_skip_no_brace("tcbposterset");
+    extras_skip_no_brace("tcbstartdraftmode");
+    extras_skip_no_brace("tcbstopdraftmode");
     extras_skip_no_brace("tcbfontsize");
     extras_skip_no_brace("tcbset");
     extras_skip_no_brace("tcbuselibrary");
diff --git a/tests/sentence_delim_props.rs b/tests/sentence_delim_props.rs
index 3a1e5c1..6b472e2 100644
--- a/tests/sentence_delim_props.rs
+++ b/tests/sentence_delim_props.rs
@@ -76,6 +76,18 @@ fn plaintext_latex_quoted_bang_letter_is_span_safe() {
 }
 
 #[test]
+#[test]
+fn plaintext_period_then_latex_quotes_is_idempotent() {
+    // ubuntu CI seed: first pass keeps `.`` `; second pass invents `. `` `.
+    let input = ".^{`}`.`` A0`";
+    let out = format_plain(input);
+    assert_eq!(
+        format_plain(&out),
+        out,
+        "idempotence\n in={input:?}\n out={out:?}"
+    );
+}
+
 fn plaintext_quoted_bang_letter_is_span_safe() {
     let input = "\"!!a\"";
     let out = format_plain(input);