More proof that no good deed goes unpunished

[rdouglass]

I think you have to pick all you can up and then abandon (or just abandon if you have few enough pop) the planet for 1 turn then put 'em back down.

I think it's that '1 turn' where the population forgets how it was back down there on the planet. (Or they're looking out the portals and seeing many bodies floating by from whomever was left.)

EDIT: Also, ISTR that captured / surrendered population inherits all of your racial characteristics (except the atmosphere of course).