If you are following the nightly builds, or downloading code from SVN, you should erase your tmp cache (either manually do it FTP/shell or click the "purge temporary folder" from within the administration section).
I upgraded smarty, the template compiler engine that we use, and they recommend doing a clear during an upgrade. And my own blog had a strange error (Call to undefined function _smarty_tplfunc_XXXXXXXX in .../Smarty.class.php on line 1828) today, and looking at it, it certainly looks like the dynamic cache and non-dynamic cache were out-of-date from each other, though I don't know why it would have taken 4 days for that to occur, so there might be another bug. But, in any case, let me know if you see this issue after clearing your cache, as it could be a new bug in the latest version of smarty.
