bought an iPad mini 2 on eBay, the description said: "Refurbished by the Manufacturer's AUTHORIZED OFFICIAL Refurbishment facility. Normal wear of minor scratches and signs". When I opened the box, I immediately saw a discoloration on the display (see 2 photos of the iPad, turned on, and turned off). What is the technical term for this defect? How does it happen? Is it because the screen has been replaced but there is a lack of adhesion at this spot?