Quite a few .IO domains seem to be dropped after a sale. I regged a few, and sold a few, during the IO 'feeding frenzy' a couple of years ago. They seem to reappear when the renewal fee has to be paid.
It's worth keeping your eye on some keywords with this extension -- they do seem to 'pop' up from time to time
always a good idea too. I sold a name for low $x,xxx. year later i noticed was dropping, picked it back up and resold it for mid $x,xxx. I can't wait until it drops again, lol