Hi. I'm observing an issue when running the latest GNU Emacs built from
source using the lucid X toolkit; this is on a Debian machine running
X11 (build details at the end).

Starting a few months ago (this is a regression) I'm seeing that
sometimes Emacs renders some faces with an unrequested (and ugly) font.
I can usually make it do the right thing by moving Emacs windows around
or resizing them, or maybe opening a new Emacs frame. It's not
consistent, and I don't know exactly what triggers it breaking or how I
can reliably fix it.

I'm attaching two screenshots of 'M-x describe-face italic' when it's
broken and right after I moved the windows around a bit, and re-invoked
describe-face. Note the very different font. Using what-cursor-position
I can see that in the wrong case the font is

 -urw-nimbus mono l-regular-o-normal--11-79-100-100-p-70-iso8859-1 (#x70)

and in the right case the font is

 -adobe-courier-medium-o-normal--11-80-100-100-m-60-iso8859-1 (#x6D)

The latter is correct since I customized my default-frame-alist to contain

 (font . "-adobe-courier-medium-r-*-*-*-80-*-*-m-*-iso8859-1")

Can somebody give me some pointers on how to debug this to make this bug
report useful? I see the breakage many times a day every day.

Thanks.