bug#37840: Missing in the Emacs manuals:

[martin rudalics]

> Now if I have some buffer.foo open in its own frame, and then issue
> C-x m, a new message buffer pops up in its own frame, as it should
> be. However, after finally issuing C-c C-c to send the mail, the
> frame which contained the mail buffer does not disappear (as it was
> the case with the old special-display.regexp stuff), rather this
> frame shows a second instance of buffer.foo.

Can you tell me the function(s) called by C-c C-c to get rid of the
window or the mail buffer?  From what you say here, the function can
be hardly 'kill-buffer' because that would not show "a second instance
of buffer.foo".  And what is a second instance of a buffer?

martin