I have that problem and determined that it's my thumb that doesn't work right (deep cut when I was little) that keeps hitting the square thingy on my laptop... BUT I have found that if I just hit the back button, lots of times it comes back up!
oh yea, the disappearing trick, we all know that one, but just now a new one on me was suddenly I was told to log in, definatley some weird stuff going on!