Since the latest version of US² collisions seem to produce a lot of spherical fragments, I don't know wether that's a feature or a bug, also in Earth vs Asteroids, all of the bodies are perfect spheres which is not what you would expect from bodies having a maximum radius of 150km.
Also, I'm sorry for not reporting bugs as much as I'd like, and if this has already been reported (I've been busy of late, as university starts next week)