No problem.  While your failing example was 'too long', you *did* search and find the appropriate previous issue, with my inadequate response and incorrect resolution, even though closed.  I appreciate having my understanding fixed.

IDLE uses several entry boxes in dialogs.  I have partially replaced error message boxes with error messages in the dialog.  For example, Open Module (Alt-M at least on Windows) opens a dialog to open a module.  Enter a bad name and "Error: module not found" is printed in red below, leaving the cursor in the entry box so the user can correct it (or Cancel).  As is turn out, this avoids any possibility of running into this bug.  I might have run into it before I replaced most old dialog + error box uses, but I now know to watch out in those remaining.