When freecam is activated and you hold a key down which activates freecam player movement with "Allow Extra Keys" set to true the freecam player starts to move forwards and lags back as long as the key is held down

Tested on 1.16.3 with 1.10.0-dev.20200913.175041

I was confused at first of how this is supposed to work. But indeed if you are moving the free camera while you toggle on the player movement option, the free camera entity gets into a constant jitter state until the player movements option is disabled again.

I would call this a pretty minor bug, but I'll still probably fix it at some point.