OK, just putting this out there in case anyone else run into this problem - I spoke to Quarq customer service (they called back after I figured out the problem) and they said others have had similar issues and were trying to nail down the problem. Hopefully this post shows up if people are googling it.

I updated my DZero from firmware version 5 to version 10 tonight and the zero offset went from around -30 to around -2200. After messing around with the Qalvin app and the powermeter it seemed that the torque reading was inversed, i.e. it read a torque value when I back-pedalled. I toggled the torque direction in the app and now everything seems to be OK with the zero offset once again being around -30.