Slabs emit power to the block below

What I expected to happen was...:
I expected the slab with powered redstone on top not to power the blocks below, but it did, unlike previous versions of minecraft. this is a big problem for the redstoners because many machine's do not work anymore.

What actually happened was...:
The pistons below the slabs got powered

Steps to Reproduce:
1. place a slab with a piston underneath
2. place redstone on top of the slab
3. power it