Microsoft has just released the following KB which applies to BOTH ConfigMgr 2007 and 2012:
MBAM Supported Computers collection query is not updated automatically to support Windows 8.1 Preview
Symptoms
When you upgrade Windows 8-based computers to Windows 8.1 Preview, the Microsoft BitLocker Administration and Monitoring (MBAM) Supported Computers collection query in Configuration Manager is not updated automatically to include Windows 8.1 Preview-based computers.
Full details at: