Another proximity sensor issue

I did a green color conversion for a customer and for some reason with this phone and one other the proximity sensor stopped working. I wasnt worried as I have a decal I put over the sensor that usually fixes that. This time it didn't. And to make it worse I put the factory glass back on for the customer and it still doesn't work. We tried a restore, no luck.

I noticed on most of the white iPhone 4's that I have been working on that they do not have the little window over the proximity sensor that the black glass iPhones do, not sure if that has anything to do.

So basically the hardware configuration is the same as when the customer brought me the phone but it isn't working. Please help.