Demo mode resets position and inventory upon launch

The timer, inventory, and position of the player all reset upon launch in the 1.16 pre-releases and release candidates. 

To reproduce

1. Launch minecraft in the 1.16 pre-releases or release candidates while in the demo mode.
2. Open the world.
3. Either pick up an item or move your position
4. Close the Minecraft game engine completely
5. Relaunch Minecraft
   →  Your inventory and position have been reset as if you had just opened the world. However, information stored in the region.mca files are still intact.