Why does the item elevator only worked when oriented north/south?

I made a slight modification to the item elevator outlined in this video - namely, I shifted the redstone ladder after the first block forward one block to minimize the horizontal footprint.

When the redstone ladder is oriented north/south, it works exactly like the one in the video - it's completely silent and will move all items placed in the intake to the top, with nothing remaining. However, when the ladder is oriented east/west, each dropper clicks once with the first item, and an item is left behind in every odd dropper, starting at the third dropper and continuing for the rest of the elevator.

I tested all four orientation of the elevator but only included two in these screenshots. I also tested different signal pulsers and different input/output directions, with the same result. The elevators are identical except for orientation - the one with green wool on top works, the one with red doesn't. The glazed terracotta is pointing north.