OK - agree, this seems unrelated to the MUC change.
[FYI when we do ship the next update, you will still be able to set a limit for the number of days (180, 365, 1000) you're willing to load using the new system property ("xmpp.muc.history.reload.limit"). However, for existing installations it seems prudent to keep the original default in place. Daryl mentioned one test system he had that had a very large MUC history, and Openfire failed to start (after 90 minutes or so) because it was trying to load everything into memory.]
In any case, seems like we still have a memory consumption issue to deal with. I'll be nosing around, but feel free to post any additional clues you might come up with.