problems with shared calendar

Hello i have a big problem with iCal.

The users with ML (10.8.x) can only see new events in a shared calendar which are created after installing the new system.

Users with SL (10.6.x) can the all event in a shared calendar

the Owner with ML can see all events in his own calendar

I have tested serveral solutions:

- new OS-X Server

- Server with Kerio

- delete an create all shares

- tested with calendar cleaner

This is the original calendar (on a ML System):

This is the same calendar shared on a ML System:

This is the same calendar shared on a SL System: