help-debbugs@gnu.org (GNU bug Tracking System) writes:
> If you wish to submit further information on this problem, please
> send it to 6078@debbugs.gnu.org.

It appears that the bug is in fact calling text-scale-adjust which
consumes one event. Calling text-scale-increase instead fixes it.

For the working version of the program, please see the following link,
or the attachment inline.

  http://www.emacswiki.org/emacs/switch-window.el

Regards,
-- 
Dimitri Fontaine