Tkinter calls Tcl_DeleteInterp when a Tk object is garbage collected, and it registers a cleanup callback for each registered command, which according to the Tcl docs should be called upon Tcl_DeleteInterp[1]. So this must either be a bug in Tcl or something in the circumstances isn't giving it a chance to clean up the commands.

It's worth noting that Tk.destroy() calls Misc.destroy() which explicitly calls deletecommand for all registered commands. So calling .destroy() when done with a Tk instance, which is good practice in general, will also avoid this issue.

Considering the above, I'm not sure this is worth investigating and addressing...

A simple solution could be to add __del__ to Tk or Misc and have that also clean up any registered commands.