As a favor to yourself, me, and all other developers, you should not accept another interview round. 6 rounds, one unplanned, is embarrassing. Where does it end

As a favor to yourself, me, and all other developers, you should not accept another interview round. 6 rounds, one unplanned, is embarrassing. Where does it end? Personally, if they can't get their interviews right (they forgot to test for something?), I don't trust them to be a good employer. Alternatively, if you really need the job, then yes you should participate in the interview.