Observers can "BUD" redstone dusts

Like shown in the title and the screenshots, we can BUD a redstone dust with a certain formation of observers.

How to reproduce ?
Place the observers, the blocks and a piston or a redstone lamp like in the screenshots (P.S. The arrow of observers is inversed in a my resource pack).
Place a redstone dust on each buildings and break the first redstone dust.

What did I suppose to happen ?
Nothing would happen

What did it happen ?
The piston extract and retract and the second redstone dust stay on.