The default value on the gamerule screen initially shows the correct default value. Any changes that has been applied will now make it show the applied value, instead of the initial default value.

How to recreate:

1. Open the world creation screen.
2. Go to the Game Rule screen.
3. Look at any of the the tooltips and see the initial default of that Game Rule.
4. Change any Game Rule and look at that tooltip again, it remains as it initially were. 
5. Click button Done to apply and re-enter the Game Rule screen and see the tooltip for the Game Rule you changed to have the same value as you left it and not the initial default value it should have.