I'm having this problem as well. I've got 3 events showing up (1 for june, 1 july and 1 september) even though i've got events loaded in between those dates. I've searched the various threads and don't seem to be able to find a solution/fix.

I've switched to GPE Calendar until I know what to do but to be honest I prefer the in-built N900 Calendar (one of the few I suppose).