I'm trying to reproduce the bug using the following command run in a Command Prompt:

PCbuild\amd64\python_d.exe -m test -r -u all -R 3:3 -F -v --timeout=30 test_ttk_guionly

Note: I'm using https://github.com/python/cpython/pull/3019 to get --timeout feature.

Once (when I wasn't using --timeout=30), I saw test_ttk.test_widgets.TreeviewTest.test_tag_bind() stuck! But it only saw this bug twice in 1 hour of intensive tests, and so I'm not sure that it exists.

Since I unable to easily reproduce the bug, it's hard to collect more information about the program state when the bug occurs.