BCStore on Amazon just emailed me about the Moko case I ordered. I guess theres a small defect where the smart cover will turn off the device if you fold the front cover around the back of the device. Theyre going to send it to me anyways and then send me the revised version next week.
I had the exact same issue with the case I bought.
The first case I bought had a slight cosmetic defect on the front, so I contacted the seller about it and they replied within 10 minutes to say "I'll send you a new one and you can keep the damaged one" - great customer service.
The replacement case arrived and that's when I noticed the magnet issue. I tried the original case and that does it too. It's intermittent, but still annoying.
I emailed the seller to warn him in case he ends up with lots of customers asking for refunds and he phoned me 10 minutes later. He apologised and said that it was down to the design of the tablet. He said that he'd tried various case designs and different magnet strengths/positions and it was a choice of either having the magnets in there, but occasionally having them trigger the sensor when the flap is folded behind the tablet, or removing the magnets altogether and losing the feature full stop.
He offered me a choice of either having a refund or of him sending me a case with no magnets in it. As the case was only £7 and he'd sent me 2 already, I chose neither and said I'd stick with the case I have for now. He said that if he does ever solve the issue he'll send me a revised case for free - although he did also clarify that he'd tried and failed to get it to work 100% and was insistent that it's the tablet design that's the cause.
I'm interested to see how others get on with cases that have magnets in them. As the issue only occurs a fraction of the time, the magnetism must be borderline powerful enough to trigger the sensor from behind. I don't think the seller was lying to me, but just because he couldn't solve the issue it doesn't mean that other manufacturers won't be able to.