In version 25, I add a sleep before the user record insertion in user/editadvanced.php file. When concurrent requests in two browsers happen on the web page by clicking User -> Accounts -> Add a new user, and enter same user infomation and click create user. On one page, a database error is shown. The error is confusing as the user is created in the table. We could catch the error and handles it by checking if the record exists in the table, and do not report the error if the record exists.