When trying to add new users with Prewikka 0.9.12.1 the login is changed to this (where <username> is the user name entered):

['None', '<username>']

I don't know Python so I couldn't properly fix it, but I traced the problem to this:

views/usermanagement.py and templates/UserSettings.py use a hidden "login" parameter to keep track of the user currently being edited. When a new user is added, the same template is used and the HTML code sent to the browser contains those two tags:

<input type="hidden" name="login" value="None"/>
<input type="text" name="login"/>

On the POST request the browser sends back this string (with two login= parameters):

view=user_settings_add&login=None&login=<username>&language=en&permissions=<some_perms>&password_new=<password>&password_new_confirmation=<password>

And some Python magic make the user appear as described above.