Odd behavior in Workgroup Manager

We are running 10.7.4 and managing domain users (as well as local users) locally via Workgroup manager.  I can create a local group (say ad_users) using dscl but don't know how I would go about scripting the addition of 'AD\Domain Users' as 'Members' of this group.  I have already added our AD server as a search directory so it's only a few clicks to add manually, but I really need a faster solution. However, currently, if I add the group Member 'AD\Domain Users' manually under the "Members" area in WGM (using the Plus sign), I save and hit refresh and it immediately says the group is 'Not Found'.  I have seen there are reports of this behavior but don't see a fix.  Anyone? Thanks in advance!