Corners Keep Chipping Off

I've had this product for 4 months now and have thought it was great...except that the corners keep chipping off. At first it was just one corner, but now 3 of the 4 corners are chipped. I'm a professional businesswoman and this iPad mostly sits on my desk--never been dropped or handled roughly, so I can't figure out what could be happening to cause this case to break.

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