I played a world, I fell into lava and I proceeded to disconnect and reconnect to not take damage. When I re-logged in, I got teleported to the bottom of the lava. It was way harder to get out of the lava using blocks because of this bug.

To reproduce
1. Find an ocean
2. Go underwater
3. Check y value coordinate with f3
4. Disconnect and reconnect
5. Check y value again with f3
6. Try the same with lava if both y values match

Expected results: Both y values should match

Observed results: When reconnecting, the y value was significantly less than when I was just underwater.

Notice: This also occurs if you are in air.