@nab thank you for pointing to this workaround. I have to admit that the crash happens in my allocation only for one particular pack/unpack (with probably some destroy nested), and depending on previous packing/unpacking at a higher level of the widget hierarchy (this is the reason a can not reproduce it in a simple script, since I still could not figure out that triggers the difference crash/non crash for the same operation). I need to investigate better the causes.

@everybody: I do not know if general suggestions are welcomed here (maybe another thread?). I like the new changes, and these are just small differences I noted to native widget, therefore not important.

ttkBrowseEntry
- the arrow icon does not match macOS, it should be a double arrow to mimic the new behaviour
- when selected, the border of the native widget is not highlighted
- the container of the native widget is rectangular, but the corners  are rounded

border highlight
- the corners in native widgets are always rounded (even if the container is not rounded)
- on my computer, the blue of Tk is lighter than the blue of original widget (Mojave, maybe different in Catalina)

Thank you for the great work!