Outlook 2011/Office 365 doesn’t retain shared calendar settings

Hi, I have clients using Office365 exchange accounts in Outlook 2011 for Mac. They asked for a public shared calendar that all staff can see. I created a shared mailbox for the public calendar. I added the calendar to each person's Outlook2011, created a test appointment, everyone saw it. So far so good.

BUT next day the editors could no longer create appointments unless they went through the "open new calendar" process all over again, and the reviewers could no longer see new appointments being added unless they also re-opened the calendar. They could however all see the old appointments. 

I've checked settings/permissions for their local install of Outlook2011, checked settings/permissions on the server, everything looks fine. Once they re-open the calendar it works perfectly. But they are not happy at having to remember to re-open it every time they logon in order to be able to use it.

Is there a way to make sure once the calendar is opened it will retain the settings without having to be re-opened the next day?

Any ideas? Help much appreciated!