You have a mailbox server that is a member of a Database Availability Group (DAG) in a Microsoft Exchange Server 2010 Service Pack 1 (SP1) environment.
The Exchange Information Store service (Store.exe) is running on the mailbox server.
The mailbox server hosts the active copy of the mailbox database.
You try to unmount the active copy of the mailbox database.
In this scenario, the Store.exe process crashes. Additionally, when you end the Store.exe process, the timely high availability of the Exchange server cannot be executed. Therefore, the DAG may become unbalanced.
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.