When I join a local network multiplayer game, my hot bar will duplicate items but depending on which slot they are in it will overwrite the item. For example, I have a diamond pick axe in the first slot, and 20 diamonds in the second slot, when I start to use my pick axe, a second pick axe appears in slot 2 and deletes all my diamonds.
If I initiate a new game and my partner joins my multiplayer game, the same thing will happen to them, but my hot bar will be fine.
We are both on the same wifi using the same version of mcpe 0.14.2