Marc, I see one small fallacy to your suggestion. You have not allowed for the possibility that the teacher has already noticed the situation, and has chosen to deal with it by not dealing with it. To bring him in to arbitrate on the mat could put the teacher in an uncomfortable position or even to have to settle the matter in a manner that was not his preferred one. I think it would be better to discuss the matter privately with the teacher first, before putting him "on the spot".
It sounds like the initial poster has had some private communication with the teacher already. Maybe speaking to the teacher again might spur the teacher to more directly address the situation, I don't know. I think that Mary did a better job of trying to convey what I wanted to suggest. I would not be asking the teacher to arbitrate but to demonstrate to us how a technique should be done. Then it is clear to both people what Sensei would like done.