I decided the accessibility argument does not apply because a) there is only one nested menu, Recent files b) that menu can be very wide and I intend to make it longer, making it a bad candidate for staying on the screen, and c) when torn off, it did not seem accessible from the keyboard.

I decided to keep the patch as is, with tearoff disabled at the point of submenu creation.  Setting the option on root is no easier when there are multiple Tk() calls.  There may be more than one for normal Idle execution.  There are many for testing, and we want the option set for tests.