I've been emptying out planets like nobodies business by stacking my harvesters.

Once I empty out a planet I set one on auto and begin a regular route with just that one. Thus minimizing colony resource loss in the event of a capture. The fleet of harvesters then make their way to the next big payload and rinse repeat.

As for trading… my understanding is that only 1 ship can be assigned to a planet, thus I believe one of three things should happen:

1. Game gives error and asks to disband fleet in order to trade.
2. One of the harvesters makes the trade, the rest stay empty… thus wasting time when they could be put to better use.
3. It bugs and they all load up on the trade.

Either way, until I can inspect the cargo of a ship I won't be the guy trying to figure this one out.

If anyone knows, I'd love to know.