Anyone else encounter this, i killed the Griffin and got my reward, i am now by the hanged tree and still have the griffins head constantly stuck to my horse

Can't you move it to your inventory?
I've had it where I could move it to my inventory but then, not be able to drop it or sell it.
But in my current game it is working.

The Griffin's head is a trophy, and an inventory item. Just take it out of the inventory spot, if you don't like it, or replace it with another one, like the Noonwraith head, or whatever.