We just upgraded to 7.5 and noticed that when the Directory Synchronization Schedule runs it deletes all the users and then adds them back with new GUIDS. This breaks all asset associations since user accounts no longer have the same GUID. I suggest anyone using Asset and User accociations to hardware to turn off this job prior to upgrade or DO NOT upgrade at all till it is fixed.
Currently we have to mount our pre-upgrade DB and use that to fix all our Asset associations that we had. PITA.