I set up three accounts:
a) firstname.lastname@example.org -- a "role" account to host shared calendars
b) email@example.com (an administrator account)
c) firstname.lastname@example.org (not an admin account)
Users foo and bar had 'manager' access to a shared calendar called 'PTO' (personal time off) created by the role account.
Logged in as user 'foo', I created an event on the PTO calendar for July 25-26. I added 'foo' as an attendee and set the free/busy to 'out of office.'
Next I logged in as user 'bar' and created an event on July 25th. Under 'find attendees' I typed 'foo', who should show up as 'out of office', but no -- user 'foo' showed as available. This seems like a bug.
Then I reversed roles: still logged in as 'bar,' I created an event for 'bar' on the PTO calendar for July 23, and added 'bar' as an attendee. Immediately upon posting this, TWO copies of the event appeared in bar's calendar -- one on the PTO calendar and one on the default calendar. This makes sense to me. Why didn't this happen for foo?
Finally I logged in as 'foo' again and created an event on the 23rd. Under 'find attendees' I added 'bar,' and under the scheduling tab I was happy to see that 'bar' was marked as 'out of office.'
The big question is why these accounts are behaving differently. The accounts were actually created two months ago, but I can't see anything different in their configuration.
OTOH, there is one difference, although I don't know why it would be relevant. Notices and invitations for foo go to a non-Zimbra mail server, and do *not* show up within Zimbra mail. In contrast, notices and invitations for bar *do* show up within bar's Zimbra inbox (but not at the external mail server).
I believe the mail routing config is set by command-line utils. My systems admin is looking into this. But as I said, I'm not sure that would be relevant anyway.