Verified on a couple of PC's

Issue; Calender view /weekly
1. personal appointment/booking = OK !
2. Booking made "to/for me" with another attendent = Black box

Switching to Monthly view, it gets more intresting;
this SINGLE booking seems to occur at the specific date and time,
but, if I hold the mouse-cursur over the appointment, a list of maybe
50 or 100 identical bookings/subjectlines shows up.

back in weekly view, switching to text-view, same issue, probably 50
to 100 lines with the same single appointment.