Hopper only checks its first stack when transferring items out

When a hopper is trying to output items to another block/minecart, it only tries to output its first stack. For example, if a hopper's first stack is diamonds, and its second stack is iron ingots, and it's trying to output items to a chest which has each 1 iron ingot in each of its slots, it will not output any iron ingots to that chest, because it only tries to output the diamond.