Basically, the AI bypass the sacrificing of Dysons to deplete asteroid energy under the following circumstance:
If the AI is attacking an asteroid you control, and they successfully destroy a tree, creating a hole, they will begin sending Dysons in to deplete the core energy. If you plant another tree on the asteroid to fill the hole, the AI will immediately gain control of the asteroid, regardless of the progress they made with depleting the core energy.
If this is intended, I think it should be documented somewhere, or the game should prevent you from planting a tree in this kind of situation.
Thanks in advance.