Example https://commons.wikimedia.org/wiki/File_talk:I_Can_Help_Me_-No,_film_still_-1,_%C2%A9Agnes_Janich,_2009.jpg (now deleted; had {{subst:ops}}
It has a template that displays the last editor and the timestamp of that edit, along side a link to &diff=cur.
However, {{REVISIONUSER}} causes a bot's null edit be displayed as the last edit, when in fact it is not an edit which are recorded in the edit history, thereby not an actual new "revision", which these magicwords are for.
I had to do a manual purge to make it display the last 'real' editors username instead