@Nobodyman:
I think the explanation for him going back to Perfect Cell, and I'm going on the Funimation dub here, is that after most of his body was destroyed his core "remembered" it and was able to rebuild his body in the perfect form.
Oh, and also I don't remember anything about this core of his. I always thought as long as there was one cell left of him he could always regenerate. Maybe that was just a mistake of the dub or maybe I just forgot.
Don't go by the FUNimation dub. It's only a bit more accurate than the 4Kids-dub of One Piece. A bit. You're mostly safe with the major plot-points, but sometimes, even those were changed.
Example: In the japanese version, Vegeta keeps trying for ages to become a Super Saiyan. Ultimately, he starts cursing his own weakness, and his frustration with himself is what ultimately causes him to transform. It is also mentioned that having a pure heart is essential to transform, and Vegeta did it because his heart was "Completely pure… pure evil."
In the dub, they make it seem like he just gave up, and just transformed for no reason. Also, the pure-heart-requirement is not mentioned, instead they actually specifically say that it ISN'T necessary.
Example 2: In the old Ocean-dub, Vegeta claims that Goku's father was a "brilliant scientist who created the artificial moon-technique". This line WAS fixed in the redub, but it was still one of their more major errors, as watching the Bardock-special clearly proves.
Okay, I'll end it there, otherwise I'd be writing for hours. But this site has even more examples, and even that's just going over a tiny number of the script-changes in the dub: http://www.daizex.com/guides/rumors/dub_mistakes.shtml