I’ve just got a new 13 inch MacBook Air - the old design, not the new one - to replace my previous one. Very quickly the lid went all floppy and wouldn’t stay in the right position. Apple are replacing the lid free of charge, which is pretty decent of them, but the guy in the store said it was down to the weight of the hard plastic shell which I use to protect the Air from damage. He said the weight of the shell was damaging the hinge. I said that I had a shell on my previous Air with no probs and he thought Apple may have changed the hinge design slightly since I bought the previous machine in 2011. Is he right? Has the hinge design changed, because the two machines looked identical. And is it a bad idea to put a hard plastic shell on a MacBook Air?