We've been working with a set of µ sites for a university's faculties sites, and we've found that apparently after a random period of time, posts permalink redirections break, making posts unaccessible (even though pages work fine). Prior to that, permalinks work ok; regenerating permalinks rules (by going into the admin->permalinks and saving with no changes) fix the problem
Our permalink structure it's /blog/%year%/%monthnum%/%postname%/
It seems that this it's not necessarily linked with the publication of a page or post.
The sites are running on a lighttpd server.
Has anyone seen this kind of problem? Any solutions or ideas about it?