All users are displayed for '%' in search result in 'Ban User' window

When you enter some simbol in the textfield in 'Ban Users' page, appears pop-up window with the user names, containing this simbol. But when ypu add in this field '%' simbol, in pop-up appears all users.
Steps:
1. Login in admin panel and enter in Users\Ban Users window.
2. Add '%' in text field

AR: All user names appears in the pop-up window (see screenshot attached)
ER: Only user name, containing '%' should appear