I honestly have no idea. But this time around the same thing is happening to me in IE too. :- (Works fine in Netscape, Mozilla, Opera, Konqueror and Galeon, though.)
One thing I can say is try to be patient. When we convert over to the new system, the SearchNew feature will be almost totally different from the way it is now...
What I'd also suggest is that after you've read the threads that interest you, go back to the BoardIndex (the forum's main page) and click on the "mark as read" button. That way none of the threads that you didn't read will come up the next time you use SearchNew unless new posts have been made to them.
I might also suggest that you dump IE and choose to use a different browser - but that's entirely up to you.