Well, that's just it. He has a love of LEARNING.
His behavior sounds pretty darned normal and healthy to me, in fact.
One tactic that you might try (and it's not without risk, believe me) is to have Ms. Negativity, there, "talk to Mr./Ms. GiftedTeacher" about his/her motivational strategies with your son...
since THEY don't seem to have all these "problems" with your child.

Heh. Fair warning, you should probably ask the teachers in question and offer a head's up about the impending request so that the unhappy teacher doesn't go in an blindside you by presenting a laundry list of inappropriate/disruptive behaviors from your DS. (BTDT, let's just say...Grrr)
It might not actually solve much, particularly this late in the year-- but then again, it at least has a chance to do so.
In either case, your son's behavior is more rewarding to him than whatever is on offer for being compliant and participatory. I don't see how YOU have any way of changing that, and he may not either at 7-8yo.