When you search for a document in Microsoft FAST Search Server 2010 for SharePoint, and FAST Search Server 2010 for SharePoint is configured to use the Documentum Connector, the search results are displayed without security trimming.
This issue occurs because the Documentum Connector does not provide user mapping from Windows Active Directory users to Documentum users in FAST Search Server 2010 for SharePoint.
To resolve this issue, apply the following hotfix package:
2597131 Description of the FAST Search Server 2010 for SharePoint hotfix package (Fsserver-x-none.msp): February 28, 2012
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.