He could be very well growing out of it.
Im sure you know what's going on in there, but I'll explain it anyway, again.
There are three ligaments going over and along the patella. One to the left and right and one directly over it. The one who causes the locking is the inside one, who is responsible for locking the leg into position for when the horse sleeps standing. This ligament is slightly too long and therefore over eager, so to speak, it locks anytime the leg is in full stretch.
So the idea behind the square toe, slightly elevated heel is enabling the hoof to breakover/lift off the ground BEFORE the leg comes in full stretch and avoiding the lock up.
Now, thinking about what the vet suggested, cutting the ligament....uhm....no more sleeping standing up......lol.
But seriously, im all for as minimal invasive as possible, so the trim was the way to go and works like a charm.
The bolting in hand...he could have been scared to death......and therefore took off. Mine kinda froze with this terrified look in his eyes, when he locked up completely. He usually had a "hiccup " movement in that leg when it was time for a trim...didn't really lock but got hung for a split second.
Longing him as large as possible, yes, ground driving, all in an enclosed area where it's safe to let go of him if need be.