Eventually my primary window loses the ability to broadcast mouse clicks or cursor position. The only way for me to get it back, that I've found, is to completely shut down and restart that instance of WoW. Although I lose the ability to broadcast mouse, the predefined regions that I have set up for click healing continue to broadcast the mouse, even from the troubled WoW instance. Also, other instances of WoW continue to function normally and if I make them the primary then they broadcast just fine.