I have a almost 6 year old quater horse gelding that I've had for almost a year and more advanced green broke I guess you could say. His previous owners really only used him to pack out elk on hunting trips but I've been working hard with him starting over with ground work in the round pen and he's come along quite well. However when I ask him to go from a walk to a trot he gets very onery, puts his head up high and does a little hop to go into the trot and is very annoyed the whole time in the trot. He only does this in the round pen or arena and not when out trail riding. Will he grow out of this or is there something that I can do to work with him so that he can make the transition better.?