Strange piston behave

What I expected to happen was...:
The piston should not be activated

What actually happened was...:
Piston is active

Steps to Reproduce:
1.  Place piston horizontally 
2. To the right/left of the piston "face" put any support block 
3. On top of support block put Redstone blok
4. Break support blobk

fell free to contact me 

Sys info: