Magical shield of invincibility

[Kain]

Now, I've been playing this game for a few days. It's fun, but I've come upon a problem occasionaly in missions where I'll face off against some enemy ship/base/battery that appears to be invincible.

It's completely random it seems. I'm not talking about a fighter vs capship. For instance, in one of the training missions, one of the drones wasn't taking damage no matter how many times I fired and hit it. I could see it being hit. Another time, it was an enemy fighter, and after that, an AAA battery. Any ideas on this?

[Raven™]

This has happened to me too, except only on a building... not in space "so far". It was 2 sam sites, that didn't take any damage no matter what I hit them with, AGM, rockets, gun fire. This lasted for maybe 2 or 3 days in game. Finally I had killed everything else on the planet apart from the two sites... did a few space missions for about 1 day in game. Took a chance and ran a sam site mission again and they were not invincible anymore, not sure what done it.. maybe running a mission in space.. maybe waiting a game day or two. But if this happened in space on say a CA or CV... man that would ruin a campain.