I'm on a mba (mid 2011). Recently my notebook would just randomly log out to the login screen... screen goes black very briefly then my login screen appears (I would enter my pw, and everything resumes normally... opened applications still open, etc. ...same as if I had put the computer to sleep). It's happened three times since upgrading. Don't know if it's related, but never seen this on my mba before ML. Anyone else experienced this? ...or know what might be the cause? thanks.