If I have a construction with a sticky piston facing down (with a block with lever above it to activate), a Slime block below, a block (for example planks) on the Side of the Slime block and a player on that block (me), if I activate the sticky piston, the Slime block, the planks and the player will go 1 block down. If I deactivate the sticky piston, the Slime block and planks will go 1 block up but the player falls through the block. I tested it in 1.8