Dragging a selected image layer from the "LAYERS" panel to the tab of an unselected image and holding it over the tab does not result in that 2nd layer popping open so the first image layer can be dropped into it. Apparently this problem occurs for some people and not others and can even be intermittent based on much time researching it trying to find a solution. In my case, my girlfriend and I have two new MacBook pros, running two brand new PS installs, same OS on both and after days of trying can't EVER do it. However it's demonstrated on Julieanne Kost's new Lynda.com course so it CAN be done. People on the forum asking about the same thing are getting responses from people who can do it too (we just did as well). The problem has apparently been going on for years. PLEASE FINALLY TAKE IT SERIOUSLY!!