When droppers/dispensers are placed like shown in the picture, the redstone signal from the top will only trigger the dropper/dispenser in the middle. This also works with two droppers/dispensers (The middle one and another one).
This will happen if the droppers/dispensers are facing west or east only!
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Can confirm, but for droppers facing north.
Works if droppers are powered directly.

Maybe a side effect of MC-108