After reloading world with Health Boost, hearts are reset to 10.

After quitting a world with health boost (and regenerated to full health possible including with the health boost), after reloading, you should have the same health as you had when you quit.

After quitting a world with health boost (and regenerated to full health possible including with the health boost), after reloading, you have 10 hearts, regardless of the level of health boost.

1. Be in survival mode with cheats on.
2. "/effect @p 21 120 4" where **** is duration, and ## is level desired.
3. "/effect @p 10 15 10"
4. Wait for health to regenerate to full.
5. Save and Quit the would before the effect wears off.
6. Reload the same world.
7. Your health is 20 (i.e. 10 hearts), not 40 (i.e. the 20 hearts you had when you quit)