Originally posted by SiEgE:

Get a properly programmable mouse. That issue is an OS issue, anyway.

Programmable mice for lefties tend to be more expensive since there are fewer choices in what to buy. Even worse if you need an ergonomic one. And it worked fine before the update. Most games do follow window's settings, and the ones that don't get complained at quickly.

Anyway, you can roll back your game to before the update by selecting default_old in betas from the side menu.