bug#15913: 24.3.50; regression: mouse-face does not stay on (turn-off due to tooltip?)

[Drew Adams <drew.adams@oracle.com>]

The same symptom is true wherever property `mouse-face' is used, AFAICT.
When you move the mouse on top of such a zone, at first there is no
highlighting, then there is highlighting very briefly, which disappears
even when you keep the mouse in the same position over the zone.

If you move the mouse away from the `mouse-face' zone and then move it
back over the zone, you will get another brief flash of highlighting.

Essentially, `mouse-face' has lost all of its highlighting, except
for a brief flash as you move into the zone.  It should stay lit as long
as the mouse is over the zone.

I see this in `emacs -Q', but especially in my setup.  In `emacs -Q', it
seems that the highlighting disappears at the moment that a :help
tooltip is displayed.  In my setup I have `tool-tip-mode' turned off.

This regression was introduced after this build (2013-08-23):

In GNU Emacs 24.3.50.1 (i686-pc-mingw32)
 of 2013-08-23 on ODIEONE
Bzr revision: 113986 rgm@gnu.org-20130823185841-zoy6h1qk433ibrlf
Windowing system distributor `Microsoft Corp.', version 6.1.7601
Configured using:
 `configure --prefix=/c/Devel/emacs/binary --enable-checking=yes,glyphs
 'CFLAGS=-O0 -g3' LDFLAGS=-Lc:/Devel/emacs/lib
 CPPFLAGS=-Ic:/Devel/emacs/include'

and before this build (2013-08-31):

In GNU Emacs 24.3.50.1 (i686-pc-mingw32)
 of 2013-08-31 on ODIEONE
Bzr revision: 114088 rgm@gnu.org-20130901021232-sazo0qla2qgcko95
Windowing system distributor `Microsoft Corp.', version 6.1.7601
Configured using:
 `configure --prefix=/c/Devel/emacs/binary --enable-checking=yes,glyphs
 'CFLAGS=-O0 -g3' LDFLAGS=-Lc:/Devel/emacs/lib
 CPPFLAGS=-Ic:/Devel/emacs/include'

-------------------------------


In GNU Emacs 24.3.50.1 (i686-pc-mingw32)
 of 2013-11-12 on LEG570
Windowing system distributor `Microsoft Corp.', version 6.1.7601
Configured using:
 `configure --enable-checking 'CFLAGS=-O0 -g3' CPPFLAGS=-DGLYPH_DEBUG=1'