When you are in your inventory and try to switch two items by using numbers on your keyboard instead of them switching it will show the texture of both blocks but when placed they are the same.

Ex: Have stone brick in slot 1 and a repeater in slot 2. Enter your inventory and place your cursor over the repeater and press 1. The items appear to switch. Try to place the repeater that is in slot 1 and it will change to a stone brick.