Confirmed: using "ExplorerPS/2" protocol the red button on mouse is mapped as Button9 (allowing you to use it in Compiz key /apps/compiz/plugins/zoom/allscreens/options/initiate_button). Otherwise, using "ImPS/2" protocol the red button is mapped as Button2 (right button on right hand setup)
Confirmed: using "ExplorerPS/2" protocol the red button on mouse is mapped as Button9 (allowing you to use it in Compiz key /apps/compiz/ plugins/ zoom/allscreens /options/ initiate_ button) . Otherwise, using "ImPS/2" protocol the red button is mapped as Button2 (right button on right hand setup)