When attempting to add a new user, it always highlights the last user added, and one has to click the 'add user' button in order to clear the fields in order to enter the new user details - which seems really user un-friendly.
Would it be better to have the fields blank, until a user is selected in the left hand pane rather than simply displaying the user details until the 'add user' button is pressed - at the moment it gives the impression that you are going to add the existing user again by pressing the add button.
I'm not sure what would be the best compromise between showing existing user details and having blank fields to be able to add new use details, but at the moment it causes confusion as it 'looks' as though you are going to re-add an existing user before you can add a new one.