Lengthy quotes in Buddypress activity stream will expand for logged-in users but not visitors.

I expect the activity stream to work in the following way: lengthy items are abbreviated and have a "read more" link that expands them. This is precisely how it works for logged-in users. But when visitors click on the "read more" link, the whole entry collapses to nothing but a "0". That is, literally that portion of the quote in the activity stream disappears and is replaced by a zero in quotes. I'm thinking this has to be a bug. Can anyone else verify whether this is happening in other buddypress + multisite + blogmu theme environments?