This is an incredibly frustrating bug for left handed users like me that use IJKL in a mirrored fashion to WASD for playing games. And also makes for everyone impossible to use I in any case without clashing this way with the mouse movement.
Holding "I" button on the keyboard makes the mouse stop entirely working for moving the view. Instead, it swaps weapons back and forth depending on the mouse direction. Maybe some leftover debug keybind?