I had this same problem and I solved it by moving the menu bar and dock to the external display.
Here's a tutorial on how to do that:
http://www.cyberciti.biz/faq/apple-osx-move-bottom-dock-top-menu-bar-second-monitor/
Hope that helps.
Here's a tutorial on how to do that:
http://www.cyberciti.biz/faq/apple-osx-move-bottom-dock-top-menu-bar-second-monitor/
Hope that helps.