There is a known issue that if you use a non-BMP wallpaper in a roaming profile using Microsoft Windows, it will not roam with the user.  To resolve this I created a script that when used as a logoff script, it will enable the wallpaper to roam.

MoveJPGWallpaper.vbs

Further to this I would highly recommend that you implement the User Profile Hive Cleanup Service which is a free download from Microsoft.com.  The User Profile Hive Cleanup service helps to ensure user sessions are completely terminated when a user logs off. System processes and applications occasionally maintain connections to registry keys in the user profile after a user logs off. In those cases the user session is prevented from completely ending. This can result in problems when using Roaming User Profiles in a server environment or when using locked profiles as implemented through the Shared Computer Toolkit for Windows XP.

I would also recommend that you use the Microsoft Group Policy Management Console (GPMC) as this will give you a far greater level of control over your GPO’s.