Dropper redstone bug

been playing around with redstone again until i discovered this strange beviour:

I used to droppers on top of each other and a chest on top of that to transport some items from the bottom dropper to the chest on top. The bottom dropper has a comparator attached to it doing all the logic for the elevator. The Redstone looks like this:

[D][C][R]
[R][E][E]
[R][R][R]

D = Dropper C = Comparator R = Redstone E = Repeater

It is the most simple possible item elevator. The Redstone shown above powers BOTH droppers which are on top of each other and thus makes it possible to transport all items vertically since you can stack this thing endlessly.

Now to my question: When the Comparators are on the North side of the Droppstower it doesn't fully work, when they are attached to the South side it does work as intented.

What do i mean by saying "It doesn't fully work"? Once all items are done being transported and the redstone mechanism stopped because no items are left in the bottom Dropper, there is one item left in the top dropper while N-1 items are in the chest. - On the other side when puting the comparator on the South side, all items are transported to the top - not one getting stuck at the end of the top dropper.

Is this a bug? Why does this happen?

Thanks a lot! :-)