Hello,I built my quadcopter with APMcopter/Arducopter and I use Mission Planner on Windows to fly it. There are no extra external sensors such as compass or GPS or cameras - I have those but didn't install them just yet - and want to try out the basic functionality of the quadcopter.In Alt Hold mode the quadcopter flies perfectly well and when I first tried the Stabilize mode, the quadcopter also flew just fine with that. But after I landed it that first time in Stabilize mode, I can't fly it in that mode anymore.The front two motors spin up normally, but one of two rear motors doesn't spin up unless I add quite a bit of power, and the other one spins much slower than the front one. It still reacts to inputs, but when I try to lift off, it flips over since the front motors spin quicker.In the "RAW Sensor" window in Mission Planner I can see that the apmcopter software gives less power to the two rear motors than the two front motors. So the quadcopter does this on purpose, it's not a defective ESC or motor. Furthermore, the Alt Hold mode works just as well as it did before.I calibrated everything and it doesn't change the behaviour. Basically, the quadcopter behaves as if it was tilted forward (nose down), and counteracts that by giving more power to the front motors.But it's calibrated just fine and the Alt Hold mode confirms that. All inputs respond, there is nothing defective whatsoever. It seems like a bug to me, but I didn't find any other users reporting the same issue, and I can't update the software because I am out in nowhere and only have my phone with slow internet to post this question.Thanks for your help!