bug#21796:

[martin rudalics]

> I'm not sure how to apply your suggestion - ediff-window-setup-function is
> obsolete on my Emacs 24.5.

I meant doing something like

(custom-set-variables
 '(ediff-window-setup-function (quote ediff-setup-windows-plain)))

in your .emacs.

The reason is that I'm convinced that the problem you and others see
here is related to focus redirection for minibuffer-less frames.  In

https://debbugs.gnu.org/cgi/bugreport.cgi?bug=24500

I provided a scenario where C-g won't get you back to a reasonable state
either (look for a function called ‘my-other-window’).

martin