RDS 2008 R2 File Type Associations

I am trying to push file type associations for .TIFs, depending on user group. This is being attempted on a Windows Server 2008 R2 RDS server.

I am using GPP  > Control Panel > Folder Options > Open With preferences. I am using two entries with item-level targeting (one for "is in <groupname>", one for "is not in <groupname>") to apply one of the two entries to the user's preferences.

At first was having an issue with "Access is denied" showing up in the event log, when the system was attempting to apply the preference. The issue ended up being a "UserChoice" key in the HKCU\Software\Microsoft\Windows\CurrentVersion\Explorer\FileExts\.tif key. I created another GPP to delete the UserChoice key, inside the .TIF key. This dealt with the "access is denied" issue.

I can now see the GPP changing the "HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\FileExts\.tif\OpenWithList\MRUList" value to reflect the preference specified, whenever I do a gpupdate. The problem is that as soon as I double-click on a TIF, explorer.exe modifies the OpenWithList key and it's values, so that the 'system default' viewer for TIFs takes back over. I've tried resetting the system default viewer, and that just changes which program overrides my preferences.

I imagine an HKLM value is overriding the HKCU value, but I have no idea which values are override my preferences, and how to keep them from doing so. I would appreciate any sugguestions.