Those were both taken at the exact same time using 1.3.1pre3.
As you can see, the earth's atmosphere (blue) covers the moon, but Comet Wild 2's tail (also blue) doesn't cover jupiter or callisto. I know the colour doesn't have anything to do with it, i'm just using it to show what I mean.
Anyway is it possible, in the next version, to make comet tails cover objects, in the same way as atmospheres do in 1.3.1 pre3...? It would make the SL9 impacts look much more realistic too, instead of the tails being covered by Jupiter when they get close...