If you login with Health Boost Effect you only have 10 Hearts and need to recover health no matter if your health was full
(Only tested in SP)

EDIT:

also noticed that with a unlimited time effect. the after is after the login and couple of seconds gone

What I expected to happen was...:
I expected that my health is full

What actually happened was...:
I only had 10 Hearts

Steps to Reproduce:
1. Give yourself /effect NAME 21 10000 255
2. Save and Quit
3. Load world