http://bugs.winehq.org/show_bug.cgi?id=34998
--- Comment #1 from Henri Verbeet hverbeet@gmail.com 2013-11-26 06:08:05 CST --- I think the issue here is that it's not clear how those additional buttons should be visible to the application. In the API there are 5 real buttons (left, middle, right, xbutton1, xbutton2) and 4 pseudo-buttons for vertical and horizontal scroll wheels. It is my impression that usually the additional buttons are mapped to some virtual key by the driver software that comes with the mouse, and that there's no standard way to do that, but I don't have the hardware to test that. Note that you can do something similar with e.g. xmodmap though.