I notice that whenever there is a containment field with enemies on the other side, sometimes they dissapear. One time I was going through Kashyykk (part 2) and there was a purge trooper, several EVA troopers, a rocket turret, and a stormie commander on the other side. The next time through (after I died :P), I saw them all just before the field came up.... but shortly after the field went up, they dissapeared. All that was left was the rocket turret.
They seem to have dissapeared shortly after I used the force to pull open the wookie cage on the other side of the field. The wookies never came out, but the troops dissapeared!