Raw mouse input inconsistent when riding on mounts

With the raw input option on, there is a noticeable difference in how mouse input feels when riding a mount (minecart, horse, etc.) versus standard gameplay. Hard to attach a video as it's hard to consistently do the same mouse inputs.

Reproduce:

1. Turn off raw input.
2. Return to the game, and move your camera around normally.
3. Ride a mount. Note that sensitivity feels about the same.
4. Turn on raw input.
5. Repeat steps 2 and 3.
6. ! Sensitivity feels different between those steps.