Slightly different engine, but my 325 read 1qt low when I put 6 bottles in. I put in 1/2 the bottle and it read .5 qt low and full when I finished the bottle. Maybe your sensor is messed up. Wouldn't surprise me one bit.
'06 Arctic Metallic 325i | Sport Package | 6MT | Dinan Stage III suspension | Dinan exhaust | 330i manifold swap! Click here!
| Active Autowerke tune | 135i Brake Calipers | Deiselboost caliper brackets | E46 M3 front rotors