It's javascript trickery.
Disable javascript and the site shows up as usual. But if you try to post anything there it won't work until you re-enable javascript, which takes you back to the blank white screen.
So I've set javascript to disabled on that site and won't be posting anything on PW any more, though I'll probably continue to read it for a while. But it'll start sliding down the drain even faster now than it was before so I don't know how much longer it'll be worth the effort...