When you have dispensers set up in the formation below the first iteration of Redstone signal they receive they act normally. Any other signal they receive beyond that makes some of the dispensers not operate ( in this example only one did on the left) the dispensers then reset and operate ag after one signal input only if they had been updated (i.e.. by a nearby block being replaced)

I've tested this with both items and TNT in the dispenser and I expect it operates with other objects too. I took a picture with the F3 menu open incase that is needed to help replicate.