A couple months ago the software got tweaked to display history info (but not contained text) of deleted revisions to any and all random visitors. In the last few weeks we've gotten a rash of complaints about edits being made with private, embarrassing, vandalistic, libelous, etc stuff in the edit summaries etc, and of course deleting the revisions from the wiki still shows them to everybody.
For the moment I'm shutting off this ability (restoring the pre-August behavior) until we get more fine-grained revision deletion / scrubbing in place. I've added a permission key to control it, 'deletedhistory', so if there's a need to turn it back on this can just be added to the '*' pseudogroup in the config to restore the previous behavior.
-- brion vibber (brion @ pobox.com)