The Bazaar Math coding is completly broken. Here is how to get 23% max health increase with the 10% Option.

Imagine a pig with 7853 health getting the 10% bonus health level up option. 

If he has the silver belt in stash (+50% max Hp), he puts it on to get 11,779 hp, then gets the 10% level up and should jump up to 12.957k.

But he doesn't because the belt calculates the max health now again, so the 1,177 bonus health gets added to the original 7,853 health, then gets increased by the belt by 50%, so he now has 9,030 health and then the belt increases it to 13,546k.

But it gets worse. When you remove the belt, it removes the ORIGINAL 50% from the 7853 health increase, and you are now at 9,620 HP.

So, because of the weird Coding Math, you now get a around 23% increase instead of the 10% Max Health increase.

UPDATE: It seems like it was just a visual Bug and it fixes itself the next hour, ty to u/Fovlsbane for noticing, but i am still right that IF it really was staying at 9620 it is coded weird/wrong. Not sure why nobody is getting that but oh well.