Droppers or dispensers placed next to each other and powerd from above react incorrectly

if you have 2 dispensers or droppers next to each other and at the same time powerd the block above them, at the first pulse they both fire, but every pulse afte only oner fires.

I made a screen shot with an observer clock and a row of droppers, there you can see that half of the droppers doesn't fire.

 

a way to mimic it slowly is by place redstone blocks above it in the following order:

1. place above 1 (it fires).
2. place above 2 (it fires).
3. remove above 1.
4. remove above 2.
5. place above 1 (it does not fire).

if you give dropper 1 an block update between step 4 and 5, it will fire at step 5.