Hi, I'm a MacTeX 2011 user.  I was working on a document that used 
expl3, then I decided to run the TeX Live Utility to update my 
installation.  After updating I could no longer build my document. After 
a lot of trial and error I think I've come up with a minimal example to 
demonstrate my problem:

~~~~~~
\documentclass{article}

\usepackage{expl3}

\ExplSyntaxNamesOn
\ExplSyntaxNamesOff

\begin{document}

Colons break: boom!

\end{document}
~~~~~~

	Here are the errors I get when I run pdflatex over that:

~~~~~~
! Missing $ inserted.
<inserted text>
                 $
l.10 Colons break:
                    boom!
! Missing $ inserted.
<inserted text>
                 $
l.11
~~~~~~

	PRIOR to updating today, the $Id$ substitutions in my installation 
indicated I had something like expl3 from SVN revision 2246.  That 
revision worked fine with the above example.

	My newly-updated version of the LaTeX3 packages as well as the latest 
version from GitHub both produce the same errors as above.

	When I use \ExplSyntaxOff instead of \ExplSyntaxNamesOff, or if I copy 
in the definition for \ExplSyntaxNamesOff from r2246, the above code works.

	Is this my fault or is this a bug?

Thanks,
Dale