So that's 2 people in this thread. Basically looks like a small number of units basically have a hardware fault then. Unlucky I guess. I really hope the store can just swap mine straight over.
Just wondering if anything else could cause it. Do you guys use a case with your 4S and if so which one? I'm using a rocketfish case which is basically like a rubber bumper with a clear plastic back. Obviously it's not design specifically for the 4S but definitely no part of the case is covering the buttons or anything and it's not too tight.
I've been using the phone daily for music and using the volume buttons and never noticed the problem until today when it suddenly started happening. Now it happens virtually every time I try to do anything with the phone.
I actually thought about this as well - I'm using an InCase Slider with mine. Nothing's touching the buttons, but I did wonder if it could have perhaps exacerbated a pre-existing design flaw or something.
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So a Genius "immediately agreed"? Tell you what, I'd fire this genius immediately if it were up to me.
I have a iP4 that's never had this issue. It started happening just now with iOS5. Happened to me just once actually since I upgraded the OS. Definitely not a hardware issue.
Good thing it's not up to you, then.