What's the algorithm for carrying out a "load all minerals" order? My impression is that it fills the cargo with whatever's "first" (I'm not sure if that's duranium or something else) and then gets some other mineral if there's still room. I would love it if there was an order which would instruct a freighter to try to load equal amounts of each mineral present (still limited by actual availability, reserve level, etc) instead of filling up in this manner.
One of the things I'm trying to do is have freighters constantly cycling between my two main shipbuilding worlds, with "load all minerals" and "unload all minerals" orders, the idea being that each planet's reserve levels will be met. So if planet X is low on gallicite and planet Y is low on neutronium, these orders will eventually bring each planet up to its reserve level with minerals from the other planet. That doesn't work, though, if the freighter fills up each time with duranium and never loads any neutronium or gallicite.