When you get 2 of the same type of armour, sometimes they stack.
MCPE-7177
Stacked armour in severs!
Resolved
Invalid
0
(Unassigned)
Unconfirmed
Tablet - Android - Other (Specify in description)
0.8.0, 0.8.1
Retrieved
This is invalid because in vanilla, there is no way to get chainmail armor and you used outside sources