When players have more than 10 hearts current health (which is possible when wearing armor with generic.maxHealth attribute modifier) and then log out, they will only have 10 hearts left when they log in.

I don't know why minecraft doesn't handle this properly, but solving this problem will be up to us. The best way is probably to create a separate mini plug-in for this.

The project has been approved: https://dev.bukkit.org/projects/remember-health

I created a separate plug-in for this, which is not awaiting moderator approval.