[TechniSol]

Could be a coating on a window refracting light, or selectively passing IR in just the right frequency range to overload the IR and swamp the detectors. Could just be heating from IR/sunlight and messing with a marginal component or three. Or, if you prefer government sponsored explanations, it was Venus refracting off swamp gas... Keep it cool, try to keep it out of full on bright sunshine and I'll bet the problem won't be one at all. Maybe the diffraction layer for the front lighting(if the reader in question has one) is acting like a lens and focusing heat on the e-ink display.

It'd be interesting to stick a Touch and a Glo in the same situ and see which gives up the ghost first.