I think I found a...well...not a bug exactly, but more like an oversight in Custom On Equip Eval, that has to do with the way it's doing order of operations;
If you have a piece of equipment that increases Max HP, and adds +X current hit points when equipped, then removes those extra current hit points when unequipped, so long as the character unequipping it is injured at least X below Maximum HP, it works fine, but if the character is at full HP, they end up at full HP -X after the item is removed, because the change to Max HP is getting processed before the Custom On Removal code. Sorry, I know that's clunky.
Examples;
Character with 10/20 HP equips armor that adds +4 MaxHP. Custom on Equip heals +4 HP, so his new hit points are 14/24.
When he removes the armor, Custom on Remove subtracts back those 4 HP, so his hit points go back to 10/20.
Character with 20/20 HP equips armor that adds +4 MaxHP. Custom on Equip heals +4 HP, so his new hit points are 24/24. This part works fine.
However, when he removes the armor, his maximum hit points are first reduced to 20, which sets his current hit points to 20 (because it was over the maximum), then removes an extra 4 HP, putting him at 16/20.