Hello my name is Ismael and I'm from México. My steam tag is: Ismaelvr_rvi.
This is a really specific bug. I'm going to list the instruction to do it. it can be done when you have finished a match.

Steps to reproduce the bug.

1.- Play a match.
2.- When you finished it. return to lobby.
3.- Now in lobby. click on options. and go to controls.
4.- I just try setting my mouse sensitivity. So move the sensitivity.
5.- click in back instead of apply. It ask you if you want to save the changes.
6.- Click "Save".

Bam. The mouse pointer has gone, and if you press "Esc" key. you can see the menu as if you are in a match. but you are in the lobby..

I'll show with an image..


I hope it can help you... Thanks for your time and for choosing me to play the Beta. You are doing a great job.