Copper slabs (I don't know about other slabs) are placed at places they shouldn't be placed at. For Example: Trying to place a lower slab onto a lower slab places it towards the right direction but not as a lower slab but as an upper slab. Sometimes you can't place two slabs into each other to form a full block but instead the slab will be placed next to the slab you try to place it onto. I hope this gets fixed very soon. It affects me a lot.