Eh tried it in Opera(set to allow popups from site, turned off popup blocking in quick prefs, no ad-blocking junk, etc), it happened again, and something yet again must be up on their end if even the 0 point items(lame wallpapers, the widget, etc) are turning up a blank "you are done, follow these instructions" page.
I'm not ever sure that, although it got my address, even the free Coke Zero gave the same thing & nothing showed up in my account's history(which was odd as last year the zero point, free 2 liter did show up in rewards status).
Oh well, even if it is a screw-up on their end, from time to time I'll just keep trying the 0 point items to check and see if they fixed it....
EDIT: Hmm, going to it directly from the rewards and sweeps tag doesn't seem to have this problem. Reminds me of one programing class I had where there were two ways to go about having the program do the same action, but only one way worked while the other had a bug.