Okay so i noticed something.
In the haunted tower, right when you go up the stairs after the exorcist with the misdreavus, I get into a 2on2 battle.
The thing is: only my Furrets got HP left, so the battle starts but i get 2 Furrets, even though I only have one. Both of them being seen as individual pkmn, but having identical PP.
When i look at my team, while in battle, my Fukano is also doubled and has taken place of my furret.
On top of that, if i return to the battle, after watching at my team, my own pkmn disappear and also will the game show me Fukanos name instead of Furrets (moves are still Furrets though).
After the battle is over, it seems everything cooled down again.
I got curious so i switched Furrets position from #4 to #1, result: my (fainted) Gyarados, is suddenly alive, with 0 hp. It will be ignored by the foe and it wont react to given commands.
If my furret now dies, its counted as a loss.
EDIT Even with two of the same kind, if the original dies its a loss. Again: The copie wont be attacked, but it can use its moves (under the condition there are PP left)
Tried this a couple times, its always Furret (or the pkmn alive) and the pkmn on #4.
So yeah, just wanted to share this with you, dont know If anyone else noticed. Its not much of a bother, it helps actually, but yeah, should be fixed.
Even though i doubt you can abuse this bug in any smart way.
Screens as attachment