So digging deeper, wsmouse is a serial mouse abstraction of our usb mouse. It's in this abstraction that the mouse click events are being incorrectly interpreted (due to flaws in the mouse design).
<p>The xev command will give you an idea of what's going on, what I'm seeing is a buttonPress/release event for button 4 that occurs 1-16 times BEFORE the correct button press.
Xorg is still accepting button 4 presses despite my attempts to make it ignore them using ZAxisMapping and ButtonMapping options in xorg.conf.