For this one simply give a race a PQ 30% bonus (if you want to test it more completely give yourself like a 900% bonus and use a pq 4 world) and fill up the planet.  Trade the planet and get it back and it still has the same output but you now have empty squares to refill.  Although I havn't observed research both food bonuses and production bonuses remain.  Probably all remain if those do.  You could see where this could become some 10000 bc planet with some work (hence exploit although a lot of work to do it).  Just give it to a minor, buy it back, build new buildings, sell it back, rinse, repeat.  Some metaverse players may find this worthwhile to create some mega score.  Took me a couple games to find this not sure how beta testers could possibly miss such a thing.