It's not impossible that some RIAA/whatever guy uses a Demonoid
account to poison it - after all, Demonoid is not that private as a
tracker.
And obvious signs like this just shows that it is poisoned. Either
that, or
1. Your Transmisson torrent client is a screwed piece of shyt. Get
uTorrent.
2. You see many ants crawling in and out of your router/modem. Get
a new one.
oh! and when i check the torrent's info, there is like 8++GB
downloaded (even tho my torrent is only 700MB), and yet only like a
few MBs of "Valid DL".
The jumping percentage of 46% and 47% could be that the same,
poisoned, pieces of the torrent were being downloaded and failed
the hash check, hence discarded, and your torrent client insists
that it MUST get that piece, or that every other piece is poisoned,
thus the process repeats, resulting in the fluctuating
percentage.