You have a TOS Violation of an outside tool to improve the performance of your game...
.. but your brave enough to ask here on the forum.

Sounds like the mouse is firing two buttons in order, and not the modified meta keybind of C1. Some games handle this, some handle it the other way. You have two games that handle it in two different ways. Bind the side button to something like F96 (a key that exists but isn't on a keyboard) and put a secondary binding in game to the skill on toolbar 10 to F96, and then hide toolbar 10