mystified by firing pattern

[Rusty_Nail]

I simulated a base station defending against two attack ships. With both in range and 10 direct fire weapons availabe, and multiple tracking, the BS destroyed one attacker with four rounds of null space and STOPPED FIRING, whereafter the other ship was given a free shot he never should have had. Is this normal or have I missed something? Should he not shift targets automatically when the first is dead? How can I make him do this? Under "firing strategy" I chose fire until no weapons left.