emerge system

[ventricle]

I've just reinstalled gentoo from stage 2. I have to do this over a modem, which I don't mind, just takes time.
I have noticed, however that emerge system downloads multiple versions of a package. I can't remember a specific package, but I know there was one that was about 10Mb, and it got 2 versions of it, so there's an extra hour to my install time. There were multiple packages this occurred on.
I'm guessing this is not an error, so I was hoping someone could explain why this duplication is needed?
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[LRU]

[blubber]

Maybe to other packages depand on seperate versions of your double package... That's why portage uses slots