User blog comment:BertH/User rights updates for Forum and Message Wall/@comment-3123266-20150124160134/@comment-452-20150124185104

Yeah, I spotted that too, perhaps it was to allow rollback users the ability to remove vandalism before they decide to make moderator.

Although it's strange that they hardcoded it as "If you can rollback, then you can also walledit", and not just add walledit to the rollback group.

They may remove that part in future, now that moderator exists.

Edit: I checked Special:ListGroupRights, and the only group that has rollback and not walledit</tt> is the rollback</tt> group.