Item stacks of one that are present in the dropper will allow it to drop that item an infinite number of times.

For whatever reason, the last items will not be removed from its inventory once dropped, and can be retrieved from its GUI, however breaking the dropper will not drop the phantom item. Those duplicated items dropped however are real, and will persist through reloading the world.

With a one tick clock, this is possibly the easiest to abuse dup glitch ever.