No message or presence when a neighbor from another house joins in a Creative World in Local Multiplayer.

Device: ZTE Awe N800
Note: This actually happened on version 0.15.6 before I updated.

What Happened:
I was in my Creative World on Local Multiplayer at a sleepover via WiFi ("Use Cellular Data" and "Broadcast to Xbox Live" are usually off). While building stuff, someone had access to my World, but we never noticed because the game never said "(player) joined the game" and the player was not listed in the Game Menu. The player, likely a neighbor from a nearby house, covered one of my friend's houses in my World with Item Frames and made a raised Fence over a Netherrack fire with a Sign saying "I hate (my friend's name)" somewhere in my World, and it has happened a second time (without the Item Frames) after I got rid of them a while ago. (Note: My friend's name was displayed on top of her house.)

How I Replicated the Issue:
We demolished my friend's house in my Creative World (she was planning to build a new one, anyway). In place of the house, I copied what the player/neighbor did and made a raised Fence and a Sign in the front saying "Why do you hate (my friend)?". Few minutes later, still being online, we came back to the Fence I made when we noticed that the Sign was replaced and all it said was "(****) you". There was still no sign of the one who did this in the first place.

Conclusion:
A neighbor likely used an app or hacked into Minecraft Pocket Edition to make it look like he/she never joined the game when going into a Local Multiplayer World. (He/she may also had access to the same WiFi to enter in my Creative World.)
This apparently is a bug and a security issue, and must be patched as soon as possible.

Thank you for your time.