It looks that this is continuation of bug #70528, where the same behaviour was observed. The issue is closed, but it seems that the case hasn't been resolved. Way to reproduce the bug. Run any program ...

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Code below has 1 major and 1 minor problem. Major issue is, once you push the button it visually stays pushed. Minor problem is, I run this in Cygwin. I've got an rxvt window behind the Tk window.