Symptoms
A content type in a document library is set incorrectly to NULL after you set the source of retention to Library and Folders in SharePoint Server 2010.
Resolution
To resolve this issue, apply the following update:
2597059 Description of the SharePoint Server 2010 hotfix package (Dlc-x-none.msp, Osrv-x-none.msp, Wosrv-x-none.msp): December 13, 2011
Status
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.