>>>> Isn't the main reason for this that it has never been possible to 
>>>> interact with a MBn when a MBm, with m > n, was active?
>>>
>>> Well, it's at best an indirect cause of the bug, but yes, it's the 
>>> reason why this bug wasn't visible until now.
>>
>> Put another way, is it not problematic to interact with and/or 
>> terminate a recursive edit while one or more higher level recursive 
>> edits are underway?
>
> I think "interact with" should be OK (I can see situations where you'd 
> use two minibuffers, where you copy text from one to the other), but 
> since the invocations have to obey the nesting, exiting from the 
> non-deepest minibuffer is indeed a problem.
>

Okay, so I wasn't completely wrong when I said that tying minibuffers to 
the frames in which they are created is complex ;-)

If it becomes possible to interact with lower level minibuffers, typing 
".emacs RET" in a lower level minibuffer that was previously created with 
"C-x C-f" would open the file.  What would happen with the minibuffer at 
that point?  What should happen if it is entered again for example with 
C-x o?  Will it become a Schrödinger minibuffer that is neither alive nor 
dead?

>> Do you think the recipe with more than two frames I just sent 
>> demonstrates a bug?
>
> If you're referring to the recipe to which I responded, then yes.
>

I'm not sure what you mean by "the recipe to which I responded".  I meant 
the recipe I sent about an hour ago.