Let's say there is a block at 0 5 0 and 1 6 0 and I place redstone dust on top of these two blocks.

When the redstone dust on top of 1 6 0 is destroyed by a piston pushing a block at it,the redstone dust will break,but the redstone dust on 0 5 0 "thinks" that the redstone line is still connected and remains the "going up" line of redstone.