bug#8936: 24.0.50; Incompatible change in the meaning of "other window"

[Eli Zaretskii]

> Date: Sun, 26 Jun 2011 11:29:14 +0200
> From: martin rudalics <rudalics@gmx.at>
> Cc: 8936@debbugs.gnu.org
> 
> If Emacs can't split a window I currently make a new frame because the
> doc-string of `switch-to-buffer-other-window' explicitly says that "The
> selected window will be used only if there is no other choice" and
> making a new frame _is_ another choice.  If people think that reusing
> the selected window is a better choice I can easily do that.

What could possibly prevent Emacs from splitting the current window in
two?  Only dimensions, or are there other reasons?