It doesn't sound like a ballast problem. It sounds like an issue with the wires inside the unit. You mentioned a controller, I'm assuming on-board, so it could also be a problem there. Somehow, a small amount of power is reaching your bulbs or ballast when the circuit should be open.
I'm not familiar with the light, so that may be total nonsence. Hopefully it at least shapes your research or cues someone else in, though.