bug#24030: 25.0.95; mouse-drag-region regression

[Eli Zaretskii]

> From: Stefan Monnier <monnier@iro.umontreal.ca>
> Cc: Alex <agrambot@gmail.com>,  24030@debbugs.gnu.org
> Date: Sat, 23 Jul 2016 13:17:09 -0400
> 
> > that creates a buffer-local binding for it.  That is why select-window
> > gives deactivate-mark a non-nil value: select-window makes the
> > window's buffer the current one, which assigns buffer-local values to
> > all of it variables, including deactivate-mark.  Then this
> > buffer-local value is being examined by mouse-drag-region.
> 
> Indeed, this is a problem here because of have a "stale" setting of
> deactivate-mark.

How did it become stale, though?  It was supposed to be reset by the
command loop when the "C-h f" command returned.  Why wasn't it?