User blog comment:Kirkburn/Technical Update: July 18, 2016/@comment-24014422-20160719121116/@comment--20160719121909

The real rollback does vanish from Special:WikiActivity. You are more than likely talking about the dev rollback script that mimics an actual rollback for users who want to feel important by roll-backing edits on communities they are not administrators/rollbacks on. I've never encountered a real rollback sticking in Wiki Activity.

The dev script rollback does not disappear from WikiActivity because it is not the "same" rollback that admins and such have.