Space Monsters ask for Partnership

[Pablo]

Hi eberybody.
I am in a humans vs. AI DevNull game with the Monsters.
Players/max: 7/7
Quadrant size: Medium
Computer players: Medium
Computer difficulty: High
Computer player bonus: Medium
Neutral empires: No
In turn 50 the Space Monsters asked all human players for a Partnership treaty. All other AIs stayed at War.
I did a quick search but couldn't find any other similar cases here. A bug?
We accepted the treaty just to see what happens next. In a few turns we will declare war to them as it is not a fun game to have Monsters for partners