As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
(CAN) WHILE OPERATING THE APU ON THE GROUND CROSSFEED WAS SELECTED TO CORRECT A GROWING FUEL IMBALANCE. SHORTLY AFTER SELECTING CROSSFEED FUEL WAS COMING FROM THE ENGINE DRAIN MAST. CROSSFEED WAS IMMEDIATELY HALTED AND FUEL VENTING STOPPED.