Editor re-creates fbm subfolder with model textures already existing in project

Hi,

I'm running Unity Editor 64 bit (5.0.1f1).

After importing an existing unity package (https://www.assetstore.unity3d.com/en/#!/content/7673), I moved the DefaultAvatar model, texture and material files in different folders (Assets\External\MecanimDefaultAvatar\Models, Textures and Materials).

Sometimes (not all the time, but can't find the repro steps), Unity Editor re-creates texture files in fbm subfolder for the model, even though they already exist in the project.

I've verified both in editor with "Select Dependencies" menu and in the meta files (checked GUIDs) that the newly created files are not referenced by anything.

'Material Search' is set to 'Recursive-Up' in the model import settings, and using 'Project-Wide' doesn't fix it.

I've exported a minimal package including the model + materials + textures + animations in their new folders (no fbm subfolder). If I import it in a clean project, when exiting the editor, it will automatically re-creates fbm subfolder including the duplicated textures.

I don't understand what would be the usefulness of recreating those textures that nothing uses. Surely it should find those already existing textures & materials.

Is it a bug?

Thanks,

Max