When we moved to GW2012 one of our departments that uses a Multi User calendar (5 users in total) noticed some strange display issues.
When User1 is looking at her Multi User Calendar, the client is displaying her appointments in User2's column as well. But if you look at User2's Multi User calendar, you don't see any of User1's appointments in User2's column, so it appears to be a display issue with User1. This same issue is happening with one other user.
All users are on Client 12.0.2, Build 108211 . Interestingly if we look at the calendar on a machine running the GW8 client this display issue does not occur. I have also gone as far as rebuilding the calendar from scratch but this hasn't changed anything.