George, I am not certain what caused this problem, but offer a thought or two. If the case were made of vinyl material, it could be the degradation of the material causing it. Think of the coating of your windshield from the gases from the vinyl dashboard.
It could also be formaldehyde gas from the adhesive in the case.
Best,
John


Humble member of the League of Extraodinary Gentlemen (LEG). Joined 14 March, 2006. Member #1.