He didn't break the cleat, there wasn't one. How do you hold a main and a spin sheet?
I've been thinking about Greg's problem with no mainsheet cleat since I first heard about it. I think I might have tried to trim in the main to the 'right place' and tie a slip knot in it, then leave it alone and trim the spinnaker. I almost never touch my mainsheet downwind when Uni, just not enough hands.