When jumping one block up to a bottom slab from another bottom slab and then trying to use the new slab to walk up to a full block, the character doesn't auto walk up and instead freezes on an invisible floor. I am able to jump off of this invisible platform, and can even move left to right on the full block. Its very easy to fall off of, and you fall when you release the forward key. On closer inspection, when on this invisible platform, the character slowly moves away from the full block and then moves towards it in a regular interval, pulsating manner over the course of around a second. It seems there is a very big window to be able to pull this off starting from when you jump. It happens consistently and lasts past relogs and relaunches.