When you have a stack of two droppers or a dropper and a dispenser (i.e. the first dropper feeds into the second or the dispenser), you have an item in the first and then you acctivate both with the same pulse, the item "skips" the second container and is shot out of it strait away.

When this works is irregular. Somethimes it works in all directions, somtimes it works like it's supposed to (put the item into the second container). Upwards and downwards always semms to work, however.