When a player places a bottom slab on top of an ice block and walks on it, the player will slide as if they are walking on the ice block itself. Mobs that walk on the slabs will also slide.

How to reproduce:

1. Place some ice blocks down (packed ice, blue ice, or normal ice)
2. Place any type of bottom slab on the ice blocks
3. Try walking on the slabs, or make a mob walk on them
4. The player or mob will slide on the slabs instead of walking normally