OC 9.x + OSX Calendar | Inviting in shared calendars not working

Hi there,
we have a (new) problem with our shared calendars when migrating from to 9.x
used with OS X capitan, Calendar 8.0
(Hosting on shared webspace)

Before (8.2.7):
We could share a calendar with all and then all admins were able to edit the shared calendar and invite people, all where able to see it. But: invitations were not send to external users. (small problem). Invitation from personal calendars are not shared with anyone (bigger problem)
Configuration: admins could edit shared calendar, others could only see it.

After (9.x):
We can share a calendar, still all can see it, admins can edit but admins are no longer able to invite others (big problem). good: Invites are now automatically shared to invitees.
Configuration: We had to take admins out of the all group, because being in group 'all' overruled the 'being admin' and prevented admins from even editing the calendar.

Fun fact: inviting others in shared calendars work fine in the web interface. not working in OS X, calendar 8.0.

Is this a known behavior, a feature, a bug or maybe even something, I can fix by settings?

Big hug for help! :slight_smile: