> Can't reproduce it here. I tried
>
> emacs -Q --eval "(global-set-key [?\C-o] 'ff-find-other-file)"
> C-x 5 f src/buffer.c
>
> and then in the frame that displays buffer.c I did
>
> C-o
>
> But the problem did not manifest itself.
Did you see the more detailed recipe I provided shortly after the original submission?