When you jump out of a helicopter and open your parachute, the mouse will both turn the camera (freelook, enabled by default and impossible to turn off) and steer the parachute.
It should probably only steer by default, and in freelook mode, shouldn't steer at all.
Get in a Ghosthawk as passenger.
Grab a parachute.
Eject and open your parachute.
Move the mouse and observe.
Mass closing ancient tickets with no activity for > 12 months; assume fixed or too trivial.
If this issue is still relevant in current dev build, please re-post.