Redstone currents don't travel down transparent blocks such as glass or slabs

What I expected to happen was...:
The current would travel down to the other redstone dust and power the piston

What actually happened was...:
The Redstone current stopped

Steps to Reproduce:
1. Put a redstone torch or anyother way to power the redstone dust
2. Place a slab or another transparent block next to it
3.Place any other block that you can put redstone dust on next to and beneth the transparent block

4.try to continue the power to something else