Two thoughts. If your command base is powered on, the ZW-C may still see it. I had this problem over the weekend. I didn't even have the ZW-C connected to the track or the Command Base, however I could not get the handles to put power to the outputs. I had programmed the ZW-C a long while back, and it saw the TMCC signal and went into command mode on me. I unplugged the Command Base and the ZW-C worked fine.
Second, the handles on the ZW-C can slip. Is it possible your D handle slipped and is no longer turning the pot internally back to zero?
Just a few thoughts here. This controller has some complexities that make it more difficult to troubleshoot.
George