I mostly move using keyboard, using the arrow keys. This works really well most of the time.
However, maybe 1 to 3 times a day (I play probably a couple of hours on the days I play), after I mount up, the mounts don't respond properly to my keyboard moves. I see it mostly on the raptor (probably because I use it most), but also on other mounts. I will mount up and try to turn in the direction I want to move, but the mount will stagger like a drunk and refuse to turn.
Once I either a) turn the right direction using the mouse or b) dismount and mount up again, it works correctly.
My keyboard setup is Turn Left = Left Arrow, Turn Right = Right Arrow, Move Forward = W, Up Arrow, Move Backward = Down Arrow.