Magnet in case causing problem?

Hi, first post in this forum..
I have bought a macbookair 2013 and it was defective. Went to the genius bar, they fixed the back lid, (it was loose making creaking noises and such), and fixed youtube making cracking noises, etc. After it was fixed, i received a case i ordered on amazon. It is a nice case for cheap and i really like it. However, ever since i put it in the case, the camera wouldn't be recognized, even by facetime and photobooth. Also, after shutting the lid and reopening, sometimes there would be a black screen with the cursor. The case has a magnetic clip/button that holds it shut, and I am worried that the magnet caused it, or maybe it was just the machine being defected.. frustrated, i took it to genius bar again and they swapped it out for a brand new machine. I am just nervous to reuse this case, as i dont know if it was the case or not. I really like the case but if it even has a little chance of being the culprit of the issue i had, there is no way i would use it. Also, the case has no "vent" system, so the laptop does get a little bit warm after a little usage.

http://www.amazon.com/CaseCrown-Cover-Black-Apple-MacBook/dp/B004QD9E54

This is the case to get a better idea of what i'm talking about.

Thanks,

Mike