In regular conditions, a hard powered dropper will update before a soft powered dropper in the same gametick. That mean that in pic 1, if an item is placed in the bottom dropper, it will end up in the top dropper when the lever is flicked. However, when an observer is detecting this top dropper, , the update order will change, and an item placed in the bottom dropper will be shot out when the lever is flicked. This happens in various situations, and breaks common T flip flop designs, as well as making other circuits very fragile to their environnement. This also allows wireless redstone in a single chunk.

How to reproduce :

Follow steps described above and shown in the pictures.