Re: Bug when running frames on two displays

[Richard Stallman]

    mini-buffer(i.e. presses C-x C-f) or click on one of the menus, the other
    frame freezes until they are done with the menu or the mini buffer. This
    is relatively small, but it is kind of bothersome, so I figured I'd report
    it.

There's no way of avoiding this except to make Emacs multi-threaded.
That surely can be done but is not a small job.