It appears that mfunc is getting munged, at least in the following scenario:
<!-- MFUNC --> rand(); <!-- /mfunc -->
essentially, this will just display 'rand()' as text on the page, and not execute anything.
The solution for me is to just turn off minify, which isn't a big deal in my case.
It's entirely possible I'm doing something wrong, but turning off minify seems to be doing the trick for me.
PS - I thought there was a place to submit a bug report, but I failed to find the link.