I've noticed that, often after I've written a review, when I hit 'Preview', it takes me to a log in screen. I always log in beforehand, but it doesn't stick! I've found a way around it though. I just copy the review, log back in, hit 'Back' twice, so that I'm at the review entering screen, then I just paste and preview again. It works more often than not the second time. Just reporting.