Max HP attributes cancel each other out.

When dealing with multiple items with the Max HP attribute, only the latest change in max HP is performed.

For example, I have a helmet that gives +16 HP (+8 hearts) and a chestplate that gives +12 HP (+6 hearts). When I equip the helmet, I gain 8 hearts, as normal. But when I then equip the chestplate, the max HP from the helmet is cancelled out, leaving me with only 6 extra hearts, instead of 10.
Now, when I hold a sword which gives +8 HP (+4 hearts) my HP is set to only 14, despite wearing armor that should be giving more. Furthermore, when I stop holding it, all health boosts are completely cancelled, leaving me at 10 hearts of health despite wearing armor that should give 10 more hearts
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