There is a little quarter horse that I ride at my barn and he is usually a good horse, but whenever you give him any leg pressure or voice cues to get him to go faster he drops his head and pins his ears straight back. He will trot reluctantly but with his ears pinned back the whole time. But then, as soon as I ask for a lope, he might step it up, but he ends up bucking. Not huge bucks, but enough to where it is unacceptable. Does anyone know why he is doing this, and how to get him to quit? I know it might be possible that his back hurts to lope, but that doesnt explain why he gets mad being at a slow trot. Any help?