Note: I've searched for this exact issue but have not found a ticket that describes what I'm seeing.

Unexpected Behavior:

When powering the second dropper in a line of droppers facing upward, with the bottom dropper containing one item, the number of droppers that item will move varies depending on the direction from which the Redstone activation came, as well as the world quadrant in which the dropper tower exists.

Example:

When powering the second dropper from the bottom of four droppers in a tower with

• all droppers facing upward and
• in the north-west quadrant of the world (quadrant containing (-1, -1)) and
• with the bottom dropper containing one item and
• Redstone signal coming from the south

the item will move into the fourth dropper from the bottom (the top dropper).

While, when powering the second dropper from the bottom of four droppers in a tower with

• all droppers facing upward and
• in the north-west quadrant of the world (quadrant containing (-1, -1)) and
• with the bottom dropper containing one item and
• Redstone signal coming from the west

the item will move into the third dropper from the bottom.

Table of Tests:

This table shows the nth dropper from the bottom to which the item will move after activation.

Attachments:

I have attached a zip file of the world I used to test this behavior (Dropper_Test.zip) and a few screenshots of that world.