This was featrured in R5 also where users were deleting rules but the $formula count in the Calendar profile document was not resetting correctly. I posted an entry a while back on my blog about this
http://quickclix.servebeer.com/blog/quickclixblog.nsf/plinks/PWEE-5TJ37R
I would be interested to know if this fix also works for R6 as I have only tested this on R5 so far...
Paul
http://quickclix.servebeer.com