When a player is partially inside a block/blocks (known bug?), if that block/blocks is pushed up by a piston, under certain conditions, the player will teleport to the top of the block/blocks

I expected the player to be pushed 1 block upwards, remaining inside the block.

What actually happened was that the player was teleported up to the top of the block they were inside

1. Sneak, and stand right on the edge of a block that is raised off the ground.
2. Use 2 pistons to push blocks down on top of the block that the player is standing on.
3. Break all blocks that are in reach ABOVE the level of the player's head, making sure that there are at least 3 air blocks above the block at the level of the player's head.
4. Using another piston, push the block that the player is standing on upwards 1 block.
This has been tested on Bukkit (multiplayer) and singleplayer