Mouse sensitivity somehow linked to FPS?

Locking frame rate to different values will result in huge changes to the mouse’s sensitivity – lower FPS => more sensitive mouse.

Development Comment:

We were able to decouple all movement inputs from the frame rate, not only from the mouse but also from the keyboard. The game will no longer take frame rate into account when changing player position and mouse input. Fix will be available in patch 0.1.7.2, thank you for the report.