I have used this package in a small "proof of concept" site with Umbraco v. 7.1.0 RC and the property editor is used on multiple nodes on same level.

The property editor have the following settings:

I have then some content "movie" nodes, which use this property editor to set the genre.

I start with clean data for this property in all movies. And then set "Batman Begins" to belongs to following genres: Action, Crime, Drama ... and click "save and publish".

umbraco.config has updated the data ... all good so far.

<movieGenre><![CDATA[[
  {
    "value": "Action",
    "group": "Genre"
  },
  {
    "value": "Crime",
    "group": "Genre"
  },
  {
    "value": "Drama",
    "group": "Genre"
  }
]]]></movieGenre>

But then if I go to the node "Man of Steel" without doing anything else and then go back to "Batman Begins" node and see the data for the genre property it's different values that are initialised.

the values in umbraco.config isn't changed yet, but if I save and publish now, the values gets updated - and it  wasn't those values I wanted.

Actually it seems that the position is updated by 1 down in the prevalues.

1. position: Original: Action  --> changed to Adventure (1 down in prevalues)
2. position: Original: Crime  --> changed to Drama (1 down in prevalues)
3. position: Original: Drama  --> changed to Fantasy (1 down in prevalues)

So I think you are missing to add or subtract by 1 somewhere in your controller.js..

/Bjarne