Inventory issues

Hello, i own the PradiseCity server, and one of my users is stuck between creative and survival.

He never actually was in creative mode..but when he joined the server

Half of his inventory is creative..and the other half is survival.

Even when he has a full inventory..he can only remove the bottom parts when looking into a chest..

but when he pushes the inventory hotkey, it doesnt let him drag his items.

WTF?