Wikimedia Bugzilla is closed!

The userrights-interwiki right allows stewards to change any and all user groups available on a given wiki. However, the form is built as though you're chainging user group membership for the local wiki, not the remote one. Thus, when changing someone's usergroups on enwiki you have the option to change 'flood' (which isn't a group that exists for enwiki) and you do not have the option to change 'rollback' (which is a right that exists for enwiki, but not meta).

The form needs to be built properly, using the user groups from the target wiki, not the one you're changing rights from.