If he has a full tail leave it alone mate and only time will tell if this will effect him later on as it depends what type of cover he is hunting, to be honest mine has a full tail and hunts alot of bramble and gorse and has had no trouble, but others can have a real bad time of it.
Go back to basics with his training so you then know what training he has had and get as much into him as you can, if he is looking like he is loosing his head a bit make him sit and stay until he calms down.
Get yourself a good gundog book or DVD on training and just work your way through it, he is at a good age