After Service Pack 2 (SP2) for Microsoft Forefront Unified Access Gateway 2010 is installed, the Bind the source IP address to the session setting doesn't work when it is selected on the Session tab of the Advanced Trunk Configuration dialog box. Even when this optional setting is selected, TCP connections from Unified Access Gateway to the back-end published resource do not use the IP address that's defined in the Unified Access Gateway PostPostValidate.inc file. Instead, these connections use the primary IP address that's defined on the Unified Access Gateway internal network adapter.
This problem occurs because of the Session Parameter updates in SP2 for Forefront Unified Access Gateway 2010 and later updates.
This problem is fixed in Rollup 1 for Forefront Unified Access Gateway 2010 Service Pack 4.
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.