I don’t think this is a bug- simply because we’ve had a large number of folks testing with MSM an unable to duplicate this particular issue.  If it does turn out to be a bug- we’d want to switch the report over to the Public Beta bug tracker- but for now, I’d suggest posting to the Tech support thread for either the trial or the standard install as appropriate.

The most likely issue is a missing or corrupted file.  So the first thing I would try is deleting the current site files- and then triple checking you’ve uploaded a fresh copy of each of the 3 required files to the appropriate folders.  If that doesn’t do the trick- when you post to the forum, make sure to let them know which theme you’re using.  That could be in play- but my first bet is on a file being ‘off’ somehow.