When standing on a slab, with an upside down slab above me, and water on the block next to my face, i levitate into the upside down slab above me.  If i place a normal block on top of the upside down slab, i do not levitate. though the levitation forces me into the slab, i do not suffocate. if there is not water beside me, i do not levitate. i guess the levitation must be a bug.