AI suddenly stops fighting

[Matze81]

When I setup a nice dogfight mission in the FMB, everything starts out nicely with a huge furball with the AI actually maneuvering as they're supposed to. After a while, however, the AI planes on both sides stop fighting and head back to their landing field or final waypoint, although the enemy planes are still around.

They will still maneuver defensively when I attack them, but they don't fight each other anymore.
I tried assigning multiple crossing waypoints for BLUE and RED with "Attack Fighters" but it's always the same. Increasing AI awareness, bravery etc. didn't help either.

How can I setup a large short range dogfight mission (like 7 vs 12) in a way so that the AI planes will fight each other, until all of the enemy planes are shot down?