Drone camera frozen?

I really don't know what happened, but now my drone camera won't move no matter what I do.

I can get in and out Drone mode by hitting "Insert" key, but the camera won't move at all, except that it still responds to TrackIR, strangely. I tried keyboard keys, deleting/reconfiguring the joysticks buttons etc, none works. I finally realized I probably accidentally hit or changed sth that freezes the drone camera from moving? But it still responds to TrackIR, confusing as hell. 

Wonder anyone had similar problem too.