Sorry to raise this one from the depths of the support canyon.
Running 2.1.0 I found that I had a problem with redirects on Insert and Update if I was using a Session Variable as the redirect. However, if I comment out the Rel2Labs line it works.
The problem is that if I use <?php echo $_SESSION['redirect']; ?> then I get a leading slash before the URL (which obviously fails).
If I comment out the Rel2Labs line it works!