Lost Fences in my hotbar

When I'm holding a lead that is attached to a mob, and my highlighting slots are 3 fences. I place down the first one, its ok, and im left with 2 fences. When I right click the fence that's on the ground, the lead is attached to the fence but also, the game only visual a fence in my inventory. But when I place 1 fence down(the fence i was left), the other lost one suddenly appear in my hand.