Tried just now with src.fedoraproject.org/rpms/python-matplotlib-inline:

• python-sig group has admin rights
• I'm in python-sig
• Tried adding epel-packagers-sig group as collaborator on epel* branches
• Failed: can't add users of a group
• Tried adding salimma user as admin (works)
• Tried adding epel-packagers-sig group again
• Now it works

So it seems that admin rights obtained via individual memberships are currently more powerful than admin rights obtained via group membership which seem to only allow 'sudo' ing by granting yourself direct admin rights?