Software :: Mouse Button As Modifier?

As I'd like to be able to fully control my desktop with both my keyboard and my mouse, I wrote a .xbindkeysrc.scm script to make two of my eight mouse buttons work as modifiers. For instance, b:9 + wheel now changes volume.

Only problem is, I accomplish this by emulating a key press with a modifier held, and the modifier seems to stick randomly after the mouse buttons have been released.

I would be very happy if anyone could point out the errors in the script below (or with the software used, I don't know how reliable xvkbd is).

Code:
(define (display-n str)
"Display a string then newline"
(display str)

[Code].....

The first part declares some base functions for the keystrokes to be sent with xvkbd. Also, the function to reset the bindings on relesae of the modifier is here. (As you may see, I already tried to put in some code to specifically reset the modifiers, with no results.) The second part contains the default bindings for buttons 10-12 when no modifier is held. The third and fourth part specify the actions when modifiers are held, usually to send a keystroke or to run a command. The fifth part performs the bindings for the first, second and third level.