None of the consoles Nintendo have released thus far have attempted what they have attempted with this console i.e. trying to retain the same graphical prowess of a home console, on-the-go. One drawback of this is heat and it's dispersal and when things get warm inside a device, unless there is something rigid to retain the shape, warping can happen. As some have mentioned on other forums, the majority of smartphones and tablets contain glass screens which stops this happening as they give it a rigidity, but Nintendo have opted for plastic. It sounds like there is something in the middle which is trying to retain the shape but failing miserably which is why the ones that have bent, have bent there. Whether it's from prolonged play, prolonged dock play... who knows. But it sounds very much like a bad design choice and Nintendo have released various models of their consoles throughout their lifetimes, whether it be internal or external.