When you throw an item on a stairblock it will begin to jump as a slime block.
But it must be thrown at the lowest step. You can throw an item on the stair from the side and top. It will jump so long its having momentum.

strong I think i cnow why this is happening. The "hitbox" of the stair is like a full block, but the stair has a lowered part in it. But still the Stair has a "hitbox" like a normal block.
The item lands on the lower step and a tick after that the item will be pushed out of the "hitbox" and the momentum of that creates a jump.

If you make 2 stair face eachother you can make a transportation system faster than iceblocks. Go ahed and try. But the stairs need momentum to travel like the ice or it will just stop.