Open an image I uploaded and take a look at the steps:
1) We are aiming to somewhere
2) Lets focus our weapon to the middle by hitting Right Mouse Button
3) Lets zoom with our little scope (RCO) by hitting + button from our keyboards
4) Okey, now lets zoom with even longer scope by pressing CTRL + Right Mouse Button
5) And now, the point of this bug. We want to get back to last zoom, so we hit again CTRL + RMB. But it doesn't remember our zooming anymore, and goes back to section 2).