According to Cult of Mac, Apple's retail stores are no longer selling slider cases for the iPhone 4 because of what's been referred to as "Glassgate" - the scratching and cracking of the iPhone 4's glass due to trapped dirt. Even cases that are part of Apple's "made for iPhone" program are reportedly being pulled.

Glassgate may or not be real, but it looks like Apple is trying to find out. A source in the case industry has confirmed that Apple is suspending the sale of all slider cases and testing them one by one in a secret facility.

Apple is investigating whether the constant action of sliding cases on and off the glass-backed iPhone can cause scratches and eventually cracks, said the source. The iPhone 4′s back is not made from the same toughened Corning Gorilla Glass used on the front. The Glassgate issue is not affected by snap-on cases, our source said.

This is huge for slider case makers - a huge hit to their bottom line, that is. Even though making the cases is cheap, makers must invest $250,000 for the molds. Many companies have ordered big production runs in anticipation of selling them at Apple Stores, but now they're left with a bunch of cases and nowhere to sell them. For example, Mophie is rumored to have ordered over 100,000 Juice Pack Airs for iPhone 4.

Not all case makers are buying into the hype. CEO of Hard Candy Cases, Tim Hickman, is not convinced that Glassgate is a real problem, but a perception problem. (Hard Candy Cases are not sold in Apple stores, so this ban does not affect his sales).

I’ve shipped 22,000 units and not heard a single complaint. If there was a problem, we would have heard about it by now. I’m very suspect that there’s a real issue there.

It'll be interesting to see how this unfolds. Will Apple determine that Glassgate is real and permanently ban the sale of slider cases from their stores?

Have you experienced Glassgate to be a real problem? Or do you have a slider case that is working perfectly with your iPhone 4? If you're a slider-case user, are you discontinuing the use of that case until Apple reaches a verdict?