The hashing algorithm for XenForo passwords in newauth.php is incorrect. This is already fixed for the next build but, posting it here so others know about it, and can patch it themselves immediately.
Download, extract, and upload the provided newauth.php file to /admin/sources/loginauth/convert/
[attachment=36481:newauth.zip]
Make sure you overwrite the one already there.
Those converting from other software do not need to do anything.