Video: http://db.tt/vQivjeeE

When walking, sprinting or sneaking from a daylight sensor to any slab (I tested this with every slab), in any direction (including diagonally) and regardless of any nearby blocks of any shape (including above), the player moves down and back up almost instantly, and is now on top the slab. This "hole" is impossible to stay inside of, and has varying effects on mobs of various shapes, though they often seem to jump very high. It also seems to work as intended when walking, sprinting or sneaking from the slab to the sensor.I also found out that this happens between slabs and beds after recording the video. It would by great if Mojang got around to this.