I registered again and didn’t get the autologin, or the redirection to another page, just the confirmation message at the top of the current page: “Thank you. You’ll receive an email momentarily.”
In the page with the registration form, could you add this outside of the shortcode so it shows up on the page when viewed, please? I want to see if it’s actually giving the previous page’s address.
<?php echo $_SERVER['HTTP_REFERER']; ?>
You could also add this:
<?php print_r($_SERVER); ?>
You do have a PHP execution plugin active on your installation, right?