its somehow hard to describe, so i made a video:

https://www.youtube.com/watch?v=XUj1OWs2TrI

i try to describe it anyways. when you put multiple vertical redstone ladders made out of glowstone right next to each other, the redstone in the whole thing will not update properly after one point has been powered.

i tested it in 1.4.2pre since the video is from 12w42b, its still not working properly.