If a stack of 64 or less head(Pumpkin, dragon head...) is place In the Head Slot of the player by shift clicking, he will have just 64 head. But If He click with an other stack on the Slot where is the 64 head that give to the player 127 head

Manipulation to recreate this :
-Take 2 stacks of the same types of head
-put one stack with shift on the slot head
-put the second by taking it in the inventory and place it on the head.