Nevermind. I see that this is caused by how the Logitech Control Center Mac OS X driver handles the mouse. The Back and Left buttons are assigned key strokes (be default they are assigned Command-Left and Command-Right). These give the expected Back and Forward functionality in many Mac apps, but translate to Window-Left and Window-Right in Windows. Boo. Hence the Start Menu behavior when clicking those buttons.
It seems like Mac OS X doesn't respond to button's 4 or 5, because you can use the Logitech Control Center to assign a Button-4 and Button-5 click to the Back and Forward mouse buttons, respectively, but neither Mac nor Windows applications respond to this.
Last edited: Dec 15, 2006