I have a friend who trains Foxtrotters for a living. He is also a farrier. So he makes his entire livelyhood from horses. Two years ago he was working with a TWH that the owners told him "Tripped a Lot" Now this friend of mine lives in Southern Utah and his method of training is to go ride in the mountains. So he was working this horse through lots of rough country teaching it to Pick Up it's feet. After several weeks of training the horse tripped and went down, landing on my friends leg and breaking it. Put him out of work for 6 months. He sent the horse back to the owners saying, No cure, Sell him.
I don't know if you can fix the problem or if it's just something that horse has to deal with. I know watching kids grow up. That they go through ages when they are gangly and clumsey and then they bloom and seem to be so athletic and coordinated. So maybe it's a growing up thing.
There is a ranch near where I live that sells a LOT of quarter horse babies. Part of their sales pitch is that this horses are born and raised on some very rough and mountainous terrain. That these colts learn to pick up their feet as babies and that trait stays with them for life. And there are a lot of people who seem to believe that.