Redstone blocks definetely don't act as intended.
Please look at the picture before reading this.

On the picture you can see that one redstone block could trigger two dispensers in two cases.
Also, a redstone block triggers two pistons on top of each other, which is normally not possible.
(Only dispensers that were sideways could be affected)

Also, one redstone block could trigger two pistons on top of each other which is normally impossible.

I tried to recreate a couple of these happenings under different circumstances and found out, that the triggering of dispensers in the top left only occurs when the redstone block is on top of the dispensers.
This is not recreatable when the two dispensers next to each other are triggered from the side.

So basically, the redstone block seems to turn the block underneath it into a redstone source too, even if the block below is nothing but air.

What's even more strange, is, that this is not recreatable with any kind of block, it only seems to occur when the redstone block triggers a certain block, like a dispenser or piston.

The redstone lamp setup on the right consists out of one redstone block in a 3x3x3 volume, in which the rest is filled with redstone lamps, so it is entirely surrounded with lamps.
However, it only triggers lamps which it normally could trigger, so it seems that the redstone block acts perfectly normal when it doesn't trigger certain blocks like pistons.

I also made a little gif which shows you the effect in action: http://i.gyazo.com/5e15c01e12f9c8b1ce90c6abb8a2dbb0.gif