the player's view continuously "lerps" or smooths to its new position after using freelook until you stop moving the mouse long enough for the lerped/smoothed motion is fully completed. in other words, the camera will keep exhibiting a slight uncommanded movement everytime the player moves the mouse after using freelook unless the time between mouse inputs exceeds the total time for the interpolated/lerped/smoothed movement to complete.
this has been a very long-standing bug, i just never got around to making a report for it until now. :)