New submission from fhdrsdg :
Found when trying to answer this SO question:
https://stackoverflow.com/questions/53171384/tkinter-function-repeats-itself-twice-when-ttk-widgets-are-engaged
The ttk.OptionMenu uses radiobuttons for the dropdown menu, whereas the
tkinter.OptionMenu uses commands
fhdrsdg added the comment:
Ah yes, you're right that `command=self._callback` doesn't pass the new value
like it should.
Your suggestion does, but throws a "TypeError: 'NoneType' object is not
callable" when no command is given when creating the Op
