Steps to reproduce

1. Visit the User Picker (/secure/popups/UserPickerBrowser.jspa).
2. Search for a part of an email address or username of a user that exists (make sure that the email address/username start with it).
3. [BUG] Only emaill addresses / usernames that start with the entered text will be returned.

Expected Behaviour

1. You should be able to find usernames/email addresses that contain the entered text in any part of the username or email address. This was the behaviour in JIRA 5.2.5.