Duplicate username

[proyb2]

Testing on release 1.1.

0. Login as existing e.g. proyb2 as user name into the symphony CMS.
1. In the author roles, key in proyb2 as username and check any checkbox.
2. Save changes and navigate to other pages/links
3. Click the web browser back button, which will then ask "Confirm Form Resubmission", press refresh button and click the "Continue" button.
4. Now navigate to the Author Roles page. Duplicate name appear in the entries.

However, it is fine if using other username. Upon further stress testing by save changes using abcd abcd (username) a few times, my full name (James Bond) start to appear in the second entry instead of abcd abcd.