Grindstone Cannot Repair Armour

If trying to combine two identical piece of undamaged armour with a maximum durability of 2147483647 in a grindstone, the result will not appear to be a single piece of armour with a full durability. Instead, the durability of the resultant armour will be 21474834, which also means that the grindstone fails to add extra 5% durability to the repaired armour.