I'm working on creating a faction, and noticed a very problematic bug yesterday: If an air unit stores a resource, harvesting units won't be able to deliver it to them, and will just sit there and do nothing. This happens both if the harvesting unit is land or air itself. The opposite doesn't happen however, and air miners can deliver to land units.
Say you make a flying saucer which can store 100 metal. You move it next to a metal deposit, then assign a worker to mine from that deposit. Once the worker is loaded, it will look for the nearest unit to take the metal to... in this case it finds the saucer. It will walk next to it, but instead of depositing the metal then returning to the mine to continue, it will just sit there and follow the unit around... as if it's trying to unload but can't.
When both the unit which deposits and the unit which harvests are air units, the miner should definitely be able to unload. If the unit who stores is air and the unit who mines is land (or the other way around), whatever the developers believe makes most sense: Either the miner can still deposit, or the miner should ignore the air unit and look for the other nearest deposit... considering they are at different heights logically.
