Duplication Bug on Multiplayer (Local Server) MINECRAFT POCKET EDITION 0.15.4

Story:
1st statement: My sister and I were on a mining expedition inside a cavern. (Survival Mode) (I had a Silk Touch Diamond Pickaxe).
2nd statement: I died by gravel trap.
3rd statement: My sister grabbed my items upon my death.
4th statement: She put all my items in a chest and waited for my return. (No cheating was done in this world at any given time)
5th statement: I grabbed my possesions in the chest. (Only one Silk Touch DP was ever made in the current world)
6th statement: She said I forgot my Silk Touch Diamond Pickaxe and took it out the chest.
7th statement: I reassured her I had the "pickaxe" in my inventory slots and showed her it in my hand.
8th statement: She told and showed me the pickaxe. (We both had the exact same pickaxe at the exact same time in visible sight)
9th statement: We noticed the bug/and or glitch.
10 statement: We recreated the pickaxe 2 more times. (3 total duplicates of the Diamond Silk Touch Pickaxe Are now present)
11th statement: As I returned home I laid the pickaxes in my so-called "Special Chest"
12th statement: I took a picture of the 4 total pickaxes and I noticed they all had the same durability.
Note: No cheating, or switching of gamemodes was ever done in that current world, which is still being actively used by me at the sending of this bug issue.