Objects without custom split Normals Data get wrong normals

[Pheater]

Objects without custom split Normals Data get wrong normals if edited together with objects that have custom split Normals Data. i.e. objects that have gotten new normals via the Data Transfer modifier or Normal Edit modifier.

[antoni4040]

I'm not sure what these modifiers do... :P
Are they new or something?

[Pheater]

These modifiers tell the mesh what the normal directions are regardless of the shape. Great for making a bundle of faces behave like a sphere for instance. This is mainly used for game engines where polygon reduction is important. It is also helpful in baking since you can make faces behave as though they are flat even though they are not.

Some more info:

http://wiki.blender.org/index.php/Dev:Ref/Release_Notes/2.74/Modeling

[antoni4040]

Game engine modeling is not my specialty. Could you please provide a .blend file where this happens? Maybe just a few simple cubes or something.