Redstone Block powers Piston through Air (vertically)

If a Redstone Block is pushed so that it is one block away from another Piston it powers it anyway.

I noticed it when I was building a Piston,RedBlo,Piston,RedBlo,Piston...-Thing downwards an I misplaced the second Piston by one Block.

What I expected to happen was...:
That the second Piston stays unextended.

What actually happened was...:
The second Piston extended

Steps to Reproduce:
1. Place a Sticky Piston facing downwards with a Redstone Block beneath.
2. Place a Piston two Block beneath the Redstone Block.
3. Power the upper Piston.
4. Blockupdate the lower Piston.

*Notes:
-works with Pistons & sticky Pistons.
-works only downwards, neither upwards or sideway.
-works in every version since the Redstone Block was added
(tried 1.5.2 ; 1.6.4 ; 1.7.2 ; 1.7.4 ; 1.7.10 ; 14w31a)
-the facing of the lower Piston doesn't matter.
-I'm not that good with redstone so this could be not a Bug, but I asked two Redstoners: they said It would be a Bug too, and if its not a Bug why would it work only downwards?