[Droid803]

Think JFK.
He was shot in the head, and he moved TOWARD the bullet, because the exit side essentially exploded. F=ma, and since there was more exiting mass than there was entering, JFK's head moved toward the bullet rather than away from it.

Same with the Colossus. You probably shot it with a mass large enough to cause it to explode on the other side.

Either that or the physics engine is broken.

I'm more inclined to believe the Physics engine is broken
I don't think I've ever seen explosions from the other side in FS. Then again, I've never played with stupidly huge mass values.

[Krelus]

JFK's head movement was probably caused by involuntary catastrophic muscle spasm. The bullet did not contain an explosive device, so to suddenly have a force vector appearing in the opposite direction of the bullet makes no sense whatsoever.

ANYwho, I will agree with the above poster: it's just the physics engine being given something it was never intended to calculate.