I downloaded both DVD ISOs, and while the one from thepiratebay.org was little bit larger than the one from linuxtracker.org, the list of installed packages from each is identical.

(And apart from some proprietary drivers for something called an AVM Fritz!Card, on cursory inspection, I don't see any proprietary software.)

I also tried running the Knoppix installer to install Knoppix in "Debian" mode (twice) and ended up with a GRUB error 2 ("Bad file or directory type") when trying to access the kernel (or any file on the partition, for that matter) both times. So I gave up and reinstalled the distro I previously had on that partition, with no problems -- i.e. there's no problem with the partition itself. Bit of a mystery there.