As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
WHEN THE FUEL SELECTOR VALVE IS SELECTED TO THE RT TANK, FUEL IS BEING DELIVERED FROM THE LT TANK, VISE VERSA. THIS WAS DISCOVERED DURING A SHORT FLIGHT IN WHICH THE PILOT NOTICED THE RT TANK FUEL GAUGE WAS DROPPING WHEN THE LT TANK WAS SELECTED. THIS WAS LATER CONFIRMED DURING AN INSPECTION IN WHICH FUEL WAS DRAINED FROM BOTH TANKS. IN FACT THE SELECTOR VALVE IS PUT TOGETHER INTERNALLY BACKWARDS. (K)