[AUCTeX] font-locking problem

[Greg Bognar]

Hi,

I have an odd font-locking problem in AUCTeX.  When I work on Beamer slides,
sometimes the font-locking works as in the "good" version of the screenshot
attached.  The faces are:

Good version:
\begin (font-lock-keyword-face font-latex-sedate-face)
frame (font-lock-function-name-face)
\frametitle (font-lock-keyword-face font-latex-sedate-face)
< (font-latex-sedate-face)
presentation (font-lock-variable-name-face font-latex-sedate-face)
My Slide (font-latex-slide-title-face)

Other times, font-locking works as in the "bad" version of the screenshot
attached.  The faces are:

Bad version:
\begin (font-lock-keyword-face font-latex-sedate-face)
frame (font-lock-function-name-face)
\frametitle (font-latex-sedate-face)
< (font-latex-sedate-face)
presentation (font-latex-sedate-face)
My Slide No face

This seems completely random.  This is the same file, same Emacs session, same
customizations; sometimes the "good" version is turned on, sometimes the "bad"
version.  I can't tell what makes the difference (e.g., restarting Emacs seems
to make no difference).

How can I track down what the problem might be?