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.