Whenever I'm playing WoW, probably about 40 minutes in, it will minimize my game and take me to my desktop???

Why does it do that? It has never done this before, EVER! But now, all of a sudden, it decides to do this to me?

Note: This isn't a major problem for me, just a nuisance and, actually, a pet-peeve. It is mostly a problem when I'm in Dalaran (lag central) and I get kicked to my desktop which stresses my PC ^_^ I just want it to stop, thanks.