My mustang Jack has been thru "the clumsies" a couple times.
The first time, he was having a problem with being very forward. We spent a lot of time working on getting his hind feet to cross up under him and getting his weight back over his hind. As one of the other commentators mentioned, a lot of it was building up strength in his hind.
The second time was definitely a question of distractedness. He was spending most of his time paying attention to anything except his job and I wasn't giving him enough support. By working on getting him with me, building his confidence and keeping his attention busy and focussed, we eventually worked our way to where he's pretty good now.
Nuthin wrong with that horse that putting the owner in training for a few months wouldn't shape right up.