Read somewhere that you shouldn't have two vapor barriers in a wall! For example, in bathrooms where a barrier is applied before tiling. If you've also put plastic in the wall, it would be double, how have you done it?
Just one barrier, otherwise you risk enclosing organic material in a vapor-tight environment.
Of course, it depends on what the bathroom wall looks like. But if you're going to install tiles, you need to have moisture protection behind them to avoid damaging the wall. In that case, you can't have plastic further in.