So I’ve got the pdHDTV 5500 and a Hauppauge card. After adding them both to mythtvsetup and running mythfilldatabase, I only get programming data for the HD card. Even after dropping the database and starting over configuring only the Hauppauge card, I still only get HD programming info. I searched everywhere for a mythfilldatabase cache or something that may force mythfilldatbase to do such a thing without success. Finally, I log into the Zap2It site and low & behold, all my channels have been disabled but the HD channels. I re-select them all and things appear to be working now.
It appears that after you define your channels and run mythfilldatabase, Zap2It will note the channels you have an remove any you didn’t originally request.