This sounds like a driver issue. I'd recommend completely uninstalling the drivers and trying again with the latest (maybe just a bad install). If the problem persists, then I'd try some legacy versions. I've used AMD cards dating back to an old Radeon 9200 for watching live TV on my PC and never experienced the issues you're describing.
Cards I've used: Radeon 9200, X1800XL All-In-Wonder, HD2600, HD4670 (current).