Steps to reproduce:

1. Enable Customize Controls (Experimental) in Settings -> Controls -> Touch
2. Switch Joystick Visibility Option to Hidden Joystick or Hidden Joystick When Unused
3. Create/open a world
4. Go to Settings -> Controls -> Touch -> Customize controls
5. Move the joystick around to a different position (e. g. top left corner), press Done
6. Attempt to move around using a different position than the one you selected (e. g. bottom left corner)

Observed result:
You are able to use the joystick and move around regardless of where you positioned it while customizing controls.

Expected result:
You are only able to use the joystick in the area you positioned it.