You can't stack the snow slabs when you try to place it on the side of a block.

What I expected to happen was it would stack when i put the snow slab on the side of a block. Then
What actually happened was that the block or the build-up of snow resets to 1 stack.

Steps to Reproduce:
1. Get Snow from Creative inventory...
2. place down a few (i.e 3 to 4 stacks)
3. right-click on the side, the snow block should reset.