Microsoft released an update to "backward compatibility feature in Windows 7 and Windows Server 2008 R2. This update enables dynamic-link library (DLL) designed for earlier versions of Windows to run in Vista context if following conditions are true: DLL doesn't specify an RT_MANIFEST resource; DLL calls an API that uses dynamic compatibility context. For e.g., DLL calls GetOverlappedResults API.
"backward compatibility feature in Win7 and 2008 R2 detects the manifest in a DLL and sets dynamic context of a DLL to Win7 or to Vista. This enables Win7 and R2 to provide a Vista context for applications designed for earlier versions of Windows," explains Microsoft in KB980846.