I have a 2012 27" iMac running OS 10.9.4 and an ASUS VN279Q monitor. I keep trying to move certain applications, primarily games, over from the iMac's display to the ASUS monitor and they're just being incredibly stubborn. I put the application into windowed mode and tried to drag it from one desktop to another: it reaches the edge of the display and won't budge from there. I tried going into mission control and moving it over from there. It went over, but as soon as I clicked on it, it popped back over to the iMac. The only possible way I can get a game to stay on the ASUS monitor is if I go into System Preferences > Displays > Arrangement and move the menu bar over to the secondary display. Honestly, I'm not 100% sure what that does, but it seems to make the ASUS monitor the primary display and all applications default to it now. Obviously, I don't want that, I want my nice 1440p Apple display to be the center of attention, not the relatively crummy 1080p ASUS one. It appears that only Steam games behave this way. The specific games that I've tested so far are CS:GO, XCOM, and Beat Hazard (I would try more, but it'd probably be pointless to test all 79 mac-compatible games I have on Steam). Non-Steam games like Minecraft move over just fine and the same goes for pretty much any other application on my computer. This is the first time I've used a second monitor on a Mac, so I don't know if this is fixable or if it's a known problem that I'm just going to have to live with. I certainly hope it's the prior, I've always wanted to live out my dream of having a different game open on each screen. This may or may not be related: I was having trouble using multitouch gestures with my Magic Trackpad (the problem showed up the same time I noticed this issue) so I fixed it through using "killall" on the dock through terminal.