Sounds to me that you have a defective DCC socket in that one of the track wires is connected directly to a motor wire, usually caused by a stray bit of solder joining the two. A DCC blanking plug does exactly that anyway which is why it runs fine on DC.
Were you able to program it successfully on the programming track initially? I would not put a loco directly on the fully-powered track until you have.
Were you able to program it successfully on the programming track initially? I would not put a loco directly on the fully-powered track until you have.