libuser.conf, python/admin.c:libuser_admin_get_first_unused_id_type, apps/l{group,user}add.1 categorize UIDs as system/user using a hard-coded value 500. Version-Release number of selected component (if applicable): libuser-0.57.2-1.fc16
Fixed in rawhide and F16 libuser-0.57.2-1.