The food production capacity of a former and new home world is getting mixed up.
I invaded someone who was down to their last 2 planets. I hit the home world first, so the other planet became the "civilization capital".
The former home world became a regular colony, but it kept the 10mt food production capacity of a "civilization capital" instead of the normal 5mt of a regular colony. The new home world never updated to have 10mt food production. So I built a farm on that planet and didn't build one on the original home world.
I had to save and reload later. When I did that, the food production on the two planets updated, so that the original home world only had 5mt of food production and the newer home world had 10mt of food production. So it looks like that's not being updated until after the game is restarted.