bug#8530: 23.2; Button 'mouse-face property loses Bold and Italic properties

[Drew Adams]

> > Well, it's not *only* the colors, since the "box" property is
> > respected.  It seems odd that some properties are used and some are
> > ignored.

Underlining, as well.  I use underlining for `mouse-face' in some buffers that
have essentially tabular data (e.g. Dired, grep).  I put the (underline)
`mouse-face' property on the whole line, to make it easier to choose from any
column and easier on visual scanning (same reason you might employ zebra
striping: to be able to easily see what's in the same row/line).
 
> Well, the font is explicitly ignored, at least in my reading of the
> code.  Maybe that's because mouse-face was intended to _highlight_ the
> text, not redraw it in some entirely different face.  Or maybe there
> are other reasons, or even no particular reason at all.  I don't know.

>From a user point of view it is a bug, IMO.  Regardless of what an Emacs
developer might foresee as the only reasonable settings, a user should be able
to set `mouse-face' to any face or any set of face properties and have that
setting be manifested.