Hi craziedde,
I have just made a fresh install of Joomla 2.5 and SEBLOD 3.4 and followed the steps above. It works as mentioned. You can set the default user to "none" and then "click to create standard joomla content" in order to get the default Joomla form. Remember they look very similar but the admin URLs are different:
SEBLOD
index.php?option=com_cck&view=form&type=user&return_o=users&return_v=users
Core Joomla
index.php?option=com_users&view=user&layout=edit
I don't know why you are having problems on your site. How did you achieve your native joomla cusotmisation of the user content type? If I were you I would just re-do these customisations with SEBLOD (if you are using SEBLOD elsewhere on your site) - that will make things a lot cleaner and consistent throughout your website.
_jrmo