He is bucking because he is young, strong and has pent up energy. That's all. It ain't a crime and not to worry too much. He may need some bucking time, so lettig him buck it out during free lunging is cool. Even if he bucks on the lunge line, don't worry too much. Just as soon as is reasonable, ask him back up into canter. The thing that worries me about a horse that is too frisky on the lunge lline is that it's easy to pull them off their balance, especailly if the footing is slick. If he is leaning too hard on the line, then you may want to do one of two things; give it a couple of good snaps to get him to get off of it, OR give him antoher 12 inches of line, kinda suddenlike and it'll put him off balance. He won't like that. Should teach him not to trust the line as something to lean on, but there is a risk that he will loose his balance.
I did see that the horse was not mentally as with you as would be best, but to be honest, he has cabin fever and he's young, I doubt I could get him better focussed on me in that situation.
When doing the leading work, give him a tad bit more warning with your upper body (leaning forward or backward before you actaully move your feet forward or come to a halt. This will help him to be ready. He cannot read your mind, so help him with that Precue of shifting the upper body, then doing the action with feet (yours).
Don't let him get quite so close up on you and he was too far ahead of you, but again, I am not sure I could actually do better at that time.
Watch his eyes and ears to have contstant feedback as to where his though is, and do what you need to get him to give you at least one ear.
He is going to be a stunning riding partner and I sense you two will do well toghether.