Map Editor : How to make "province inserted" work?

[Twan]

I have 150 or so provinces already described (name, neighbours etc) in a map file, but forgot a withe pixel for one. I want to use the "province inserted" function but it seems it's bugged. I've tried before modyfying the tga and after, I've tried just after loading the editor, I've tried with or without the inserted province selected, etc... the function simply changes nothing. In all cases inserting a province still messes all my other provinces terrains neighbours and names.

Is the editor known to be bugged when used with very big maps (the one I'm working on has 1200 provinces) ? Is the function known to be bugged in general ? Is there a trick to make "inserted province" work ?