Current draw makes 0.5A steps

When running ArduPlane 3.6 in a MAVProxy SITL instance, the current draw does something wrong. The voltage stays pretty constant, usually stays around 12.587 but can change to 12.537. Nothing weird there. The problem is that the current draw is either 0, 1.49, 1.99, 2.49, 2.99, 3.48, or 3.98 etc. The current is making these discrete step changes as I increase airspeed, where I expect the precision to be 0.01A. How can I get the precision of the current to 0.01 and see a more continuous change in current? This is a problem for measuring power consumption.