I guess we can conclude it's the disc, as it seems to not work on both the computer + set top, and I have a working copy of the same torrent'd data.
Maybe pick up a 5 pack of some other DVD media?
And you're sure it's claiming successful data burnage at the end. It's not having an error or something, is it? Does the disc look full if you flip it over to the data side (the data will be a slightly different color compared to the unburned portion. If it's stopping halfway through, it will look like a dullish band that stops about halfway from the edge of the disc. If you can't see two colors, then it's most likely finishing all the way.)
This is, indeed, a puzzlement...
ViPERPHiSH