In two different games i invaded a system with two planets. I won the ground battle, but didn't control the system. Then everytime i invade, i win and nothing happens.
Did i miss something?

Hi,

Are you playing as Vodyani? If so, then the system turns into "hunting grounds", generating Essence until there is no more population on it.

If not, then it soudns like a bug! Don't hesitate to report it in the appropriate forum.