Why can't I change the icon on a tkMessagebox.askyesno() on OS X?

I found a solution:

tkMessageBox.askretrycancel(title, message, type=tkMessageBox.YESNO)

seems to work, but both buttons presses return False, so it's not of any use.

tkMessageBox.showwarning(title, message, type=tkMessageBox.YESNO)

does also work work, but be aware that it returns 'yes' or 'no', not True or False. It's the only real option though.

I would still be interested if anyone can tell me whether it is a bug.

CodeHunter