When using Mithral Chain Shirt and Mithral Buckler the armor check penalty is incorrect.
Mithral should reduce the penalty to 0 for both the Chain Shirt and Buckler
From https://www.d20srd.org/srd/specialMaterials.htm
Mithral
Mithral is a very rare silvery, glistening metal that is lighter than iron but just as hard. When worked like steel, it becomes a wonderful material from which to create armor and is occasionally used for other items as well. Most mithral armors are one category lighter than normal for purposes of movement and other limitations. Heavy armors are treated as medium, and medium armors are treated as light, but light armors are still treated as light. Spell failure chances for armors and shields made from mithral are decreased by 10%, maximum Dexterity bonus is increased by 2, and armor check penalties are lessened by 3 (to a minimum of 0).
But even though when hovering the item it says it's 0, when you look at the skills you still find the normal penalties (Chain Shirt is 1 because it has the nimbleness property, otherwise it would've been 2, like a standard Masterwork Chain Shirt).
I tried the other items (large shield, full plate, Mithral Garb = Chain Shirt) they all have the same armor check as a standard Masterwork item
When using Mithral Chain Shirt and Mithral Buckler the armor check penalty is incorrect.
Mithral should reduce the penalty to 0 for both the Chain Shirt and Buckler
From https://www.d20srd.org/srd/specialMaterials.htm
But even though when hovering the item it says it's 0, when you look at the skills you still find the normal penalties (Chain Shirt is 1 because it has the nimbleness property, otherwise it would've been 2, like a standard Masterwork Chain Shirt).
I tried the other items (large shield, full plate, Mithral Garb = Chain Shirt) they all have the same armor check as a standard Masterwork item