If only this HD channle have problem,maybe need to use special decorder,Would you mind using other decorder to have a test,maybe this can solve your problem.
I have already tried that and it makes no difference. It appears to be something to do with the ATI Catalyst drivers, and some people have had success with DOWNgrading their drivers to a much older version.
Anyway, I'm not looking here for a solution as I'm not likely to get one here, just informing the original poster that he's not alone.
The latest catalyst drivers, version 12.4, have solved this problem ... BUT, they have introduced a new problem whereby the HDMI driver is disabled when the TV is powered off! However, there are reports that the beta for 12.6 (don't know what happened to 12.5) has solved this problem. Personally I've solved it temporarily by uninstalling the AMD HDMI driver and rverting to the standard MS one for the time being.