When trying to use pick block function on Acacia Leaves while no other is in your player's inventory, the game will produce a visual glitch, where it will show the Acacia Leaves with a red stack number of 0. This Acacia Leaves stack will place whatever block it took the block of, and if no block was in it's slot beforehand, will not place at all. I checked previous snapshots, this bug appears in versions 15w33c and later for me.