Weird motor reversing bug

(Disclaimer: Fake lego 42171 and motor kit, but functions are literally the same and this is the only sub with technic experts to answer me) Hi, I use a servo for steering, L motor for driveshaft, a rechargable 4-way battery box (built-in IR receiver) and this IR remote. Servo is connected to B, L motor connected to C. I noticed a bug that doesn't make sense, all 4 directions of the car work individually (left, right, forward, backward). Holding down LEFT + FORWARD/BACKWARD works fine, but...