It's bug or just mistake in item description. i mean these shirts pdef,
on +0 shirt it shows 60pdef. same pdef have glorious t-shirt (from GF quest), but when you equip istina shirt your pdef is lower than with glorious t-shirt.
so where is the truth? also in one site there is description that these shirts have 48pdef, in other just item description what shows 60.