Strange question and I apologize if it's blatantly obvious. I use a 15" rMBP with a TB display and a secondary 24" display from time to time. I realized after a few times of doing this that when I do a 3 finger swipe to go between screens/apps now (when it's not connected to the external displays) that there are way more "screens" open than there are apps open. Even after restarting the computer, when I 3 finger swipe from right to left I'll get my main screen (desktop background, open minimized Twitter window), my full-sized Safari window, and then I can keep on swiping about 5 or 6 more times that results in old desktop backgrounds with no apps or programs open. Any idea what causes this?