Yeah I have the same monitor configuration and ran into the same problem. It's a unity bug, but got set to low priority so I don't know if there's any plans to fix it. The Alt key works for me as a workaround too.
** Package changed: xserver-xorg-video-intel (Ubuntu) => unity (Ubuntu) -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/772199 Title: Moving windows between multiple screens -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs