What else changed? We think the metal dome switch may have. Let's look closer.

The dome is like a really tiny jam lid or Snapple cap—you press down and it springs back up.

If anything changes about the dome—if it's cracked or deformed—the key may behave erratically. Likewise, if the prongs break or bend, the key stops working.

It's entirely possible that several of these factors are contributing to switch failures, which could explain why Apple is having such a hard time untangling the problem. Fourth time's the charm?