Consider the following scenario:
You are running Microsoft Outlook 2010 by using your user account in an Exchange Server 2010 environment.
You create several calendar groups in Outlook 2010 calendar.
You add calendar links of another user (user A) into all calendar groups.
You log on to Outlook Web Access (OWA) 2010 by using your user account.
You click Calendar in the navigation pane.
In this scenario, user A’s calendar link only appears in one of the calendar groups that you created. Additionally, when you open your Outlook 2010 calendar, user A’s calendar link only appears in the same calendar group.
This issue occurs because OWA 2010 incorrectly removes user A’s calendar links from calendar groups as duplicate calendar links.
To resolve this issue, install the following update rollup:
2529939 Description of Update Rollup 3 for Exchange Server 2010 Service Pack 1
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.