When testing out a build, I noticed that placing pistons on top of each other, all holding redstone blocks, is impossible.

The video given with this link was too big to post here:
https://www.dropbox.com/s/0fksdortb3m8imh/2017-05-27%2020-49-48.mp4?dl=0

If a powered block (a redstone block or a block powered by redstone) is placed in the configuration shown in the video, the piston will extend. There isn't that much else to say about the bug, but I know that this shouldn't happen.