The above patch by email@example.com does fix the problem for me
(although I had to expire the page caches for all affected nodes). the
use of $chunk (which appears nowhere else in the function's scope)
instead or $text in the preg_replace filter effectively erases the text
the function is passed.
This appears to be fixed already in the 4.5.8 tarball from upstream. cvs
uses a totally different $chunk operation. Perhaps it was a botched