mouse doesn't work in remote gui applications using x11 forwarding

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http://unix.stackexchange.com – I am using dual screen mode. I can use the mouse in the remote GUI applications like emacs, but it only works if mouse is located within screen 1(where windows 'start' button is located). When I move the GUI screen to the screen 2 and try to move the mouse over the application window, the window keeps running away to screen 1. Only way to keep it stay in position is to make it fullscreen in screen 2, but it still doesn't respond to any mouse event. This doesn't seem to work in any other remote GUI applications. Anyone know the reason for this?? I find it inconvenient because I can't use my mo (HowTos)