You know I have never had this problem that you guys talk about and I just have the Demo which has a more limited AI then the full game.
Normally when an enemy fleet comes in it does attack a colony UNLESS it detects a larger defensive fleet then it thinks it can handle OR unless a battle occurs somewhere else in their space and they think they need that fleet to defend themselves.
So maybe what you consider it just being stupid is actually the AI redeploying it's fleet to protect it's self from an enemy elsewhere that you are not aware of.
Because like I said the AI acts rather smart around me
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