This is probably the most obvious flaw in their capabilities. If they're moving towards a position, retreating, following a friendly, or pursuing an enemy that's out of range or that they don't have a clear line of fire towards, they won't retaliate against other enemies attacking them (except with secondary weapons when a target is in the fire arc). As long as they're moving roughly towards their goal, they should be able to turn (if necessary), without thrusting, and fire all their weapons at nearby hostiles.