Question: Vistors to our website can fill out a form to create an account. It is a CiviCRM profile, and "WordPress user account registration option" is set to "Account creation required". The username and password fields are shown above the profile but a Wordpress account is not created when the form is saved. A Contact is created, but it is linked to the Wordpress admin account (ID #1).

I attempted to replicate this on the [Wordpress Demo site](http://wpmaster.demo.civicrm.org/). I created a profile that required Wordpress registration, but it (quite reasonably) would not allow me, as the demo user, to create a page for embedding it. When I view the profile in "Create Mode", it does not show the username and password fields (even when not logged in), and no new contact or account is created.

Answer: 
Occasionally WordPress plugins can interfere with user account creation. Have you installed any spam prevention plugins recently? If so, try turning it off and seeing if the user creation option shows up on your profile. 

The reason this isn't working with WordPress demo site, is that User Creation is turned off on all demo sites. You may want to check that this is enabled on your own site as well.
As it turns out, it was a custom extension that was causing the problem. Under certain conditions the extension would generate a blank `cms_name` value. When `wp_insert_user` was called with a blank username in the Wordpress.php system backend, it returned a `WP_Error` object instead of a userID. This error was ignored by CiviCRM and the newly created Contact was assigned Wordpress ID #1.