I noticed a really weird behavior on my MacBook Pro today.
I have two of them at work, a 13" late 2011 (which I don't use often), and a 13" early 2011 where I put a SSD (which is my main computer).
So the late 2011 MBP usually stays asleep and the early 2011 (with SSD) sits on top of it. But I noticed that if I try to wake up the SSD MBP (by opening the lid) while the other one under it is sleeping, my MBP doesn't wake up. But as soon as I pick it up, it wakes.
This only happens when I open the lid when the MacBook sits on top of the other one. If I wake it up elsewhere, it works perfectly.
I don't know if it's clear, as it's a bit weird. It's not really a problem actually but it would be nice if someone could clear up this mystery (still, I actually spent some time the other day trying to understand why it wouldn't wake up, I even reset the SMC)
I thought about the magnet that holds the lid closed that could act like the iPad Smart Cover but the magnet doesn't seem to be that strong.
Best Answer
It's the magnets, they aren't super strong, but strong enough to keep the lid close firmly. The magnet sensor is probably a little bit too sensitive. To confirm this hypothesis, you could turn one of the laptops around. So the magnet sensor of the top one is over the hinge of the bottom one.