Every computer in the local administrator group (and remote desktop users group) contains a random selection of domain members. After deleting them they come back after a restart or forcing an gpupdate. This seems to indicate the problem lies within the GPO settings, but I cant find their anything which should do that. The fact that they are random members and different on every computer seems to me a local problem.
I used "Computer Configuration --> Preferences --> Control Panel settings --> Local users and groups" until recently but have removed that policy. Now I changed to "Computer Configuration --> Policies --> Windows Settings --> Security Settings --> Restricted Groups" I have there one group, with 3 users, which is a member of Administrators and Remote Desktop Users. This seems to work, as that group is added.
Now I only need to get rid off these random domain members. Does anybody know where else I can find some settings related to this. Using Google I only find information how to add members, not how to delete them.