This one's hard to explain with text, so hopefully the video and pictures do a good job.

Essentially I built a diagonal tower for one of my projects, and attempted to power it from below with only one line of redstone. I don't see a problem with this, as pistons aren't solid blocks and therefore shouldn't block the redstone signal. However the pistons do not appear to be powered by the piece of redstone visually going into it, instead they seems to be powered by both the block horizontally to them and the piece of redstone on top of it, both 2 blocks away.

To replicate the bug just build the setup in the pictures and try it for yourself.

Since the video attachment isn't seeming to work for me, I went ahead and put it on youtube: https://www.youtube.com/watch?v=CA0cqbQ0Krw