Observer activating through it's side, mainly on sticky pistons and slimeblocks.

When an observer block is connected to a sticky piston VIA slimeblock (underneath and above), the observer continually triggers the sticky piston.

What I expected to happen was...:
I believed that observer blocks wouldn't move when connected to slimeblocks, but even if they did, the observer shouldn't transmit redstone through it's sides and into the piston VIA the slimeblock.

What actually happened was...:
Long story short, the observer is transmitting the block update signal through it's sides and into the slimeblock, therefore making the piston move continually.

Steps to Reproduce:
1.) place sticky piston facing forward 1 block above the ground.
2.) place slimeblock on the sticky piston's face
3.) place the observer on the top of the slimeblock