We're running GW12.0.2 and we're getting the occasional person who is seeing appointments for other people in their own calendar when the multiple users tab (i think its called that, using localized client) is also configured.

When they are looking at their personal day/week/month overview it will show appointments on top of their own that are not theirs, removing the multiple users from the multiple user overview 'fixes' the problem but this is obviously not the correct way.
I'm not really sure what is going on here or how to fix it, has anyone experienced this before ?

I'm quite sure this began when we started using 2012 but then it was just with 2 people, for some reason it starts happening more frequently now and for no apparent reason.