When 2 droppers, call them A and B, are set up so that A is pointing into B, B is empty, and A has item(s), there are certain conditions where providing redstone power to both at once cause B to trigger slightly after A, even though they should power simultaneously. This causes 1 item from A to go to B, then immediately in the same pulse, be emitted by B. The conditions depend on the axis A and B are placed on, the order they are in on that axis, and the direction the redstone signal enters from. It is easiest to see this if A and B are pointing into each other, instead of just A into B. In that case, no matter the axis, and no matter the direction the signal comes from, this will always occur. This does cause problems in certain circuits which would be easier to build and more compact were this not the case. I have not tested if this occurs in the snapshots, so it might.