When you use Advanced Search in Exchange Control Panel (ECP) to search for recipients based on the UM Mailbox Policy filter, correct results are not returned. Additionally, you receive the following error message:
Invalid search filter
This issue occurs because, when you add UM Mailbox Policy filter and start the search, ECP sets the UM Mailbox Policy filter to an empty value, which causes an invalid attribute error when Active Directory is queried.
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.