I experimented an unusual problem : when I wanted to delete a pending post created with wp_userfrontend, WordPress told me that a was cheating because I was not de owner of the post...
After looking for the source code (file wpuf_dashboard.php, line 231), I saw that $userdata was called but unavailable in the context. I just added "global $userdata;" in the begining of the function an then all was ok.
Hope it will help,
Thank you for your great job :)