Put the summary of the bug you're having here:

Place a piston next to a slime block, place a top half-slab on top of the slime block.

What I expected to happen was...::
The piston should simply move the slime block, the slime block should ignore the top half-slab above it, because there is no physical / graphical connection between slime block and the top! (upper) half-slab

What actually happened was...::
The piston moves the slime block, and the upper half-slab above it is moved by the slime block. It is like magic, or magnetism, because there is no connection between slime block and upper half-slab above it.

Steps to Reproduce:
1. Place piston looking south east west or north (not facing upwards or downwards)
2. Place a slime block in front of it
3. Place a upper half slab above the slime block
4. Power the Piston
5. Watch the Bug