Auto-Brightness on iPad mini Retina is not working properly.

Hello! Noticed that the Auto-Brightness on iPad mini Retina is not working properly.

It works correctly only when such a dark place, then unlock the iPad brightness will be at a minimum. Likewise, if unlock iPad in a room with light, the brightness will adjust to the surrounding space.

If I turn light into a dark room, the brightness slider does not move, and stands on the site. Checked on the iPhone 5S, there problems are not present. Auto Brightness is working correctly.

P.S. Sorry for my bad english!