I'm on the mission where you have to guard the Iota ships through the asteroid belt and the shivans periodically attack.
However, once the shivans first came in, I targeted them and blew them up. All of a sudden, any white target boxes to indicate which ships were on a collision course with the Iotas were gone. The Direction and distance indicators at the edge of the screen were still there, but once I had the asteroids visible, there was no box around them, even though my wing men would shoot them.
The next time (2nd) the shivans came, I targeted them again. I noticed that while I was targeting a shivan, the white boxes were back around the asteroid. As soon as I blew up my target, the white boxes were gone again.
This led to Iota 1 being triple teamed by 3 large asteroids at once. Cool to watch.