Uh try powering the Hopper with a Wire from the other Side. You run into a vanilla Bug there, where the TileEntity tick order depends on when the TileEntity got created/loaded.
So the best I could tell you is powering all 4 Hoppers from below instead of at the same height.
Also pretty sure the description of the Support category of the Forums tells you how to submit Bug Reports without any Account whatsoever on IRC 