I have this problem as well with one of my OTA locals. I contacted dish, and they actually sent me a new reciever. It made no difference, the new reciever did the same thing. In my area, we actually have a good station engineers that use the avs forum to talk to the local OTA users. The engineer for that station said it was not a problem on their end b/c I was the first he had heard of the problem. So, he blamed it on dish and the 622. I'm beginning to think he might be right.
I'd be interested if their is a solution to the problem.
(fwiw, my setup sounds very similar to yours: onkyo receiver, hdmi, rear projection. Before the onkyo receiver I actually had it hooked up through an RCA reciever and fiber... and had the same problem. I really do think it's an issue with the 622)