When you drag material from content library materials tab to a model either in navigator or 3D view, another copy of the material is always created in material library. Intuitively I would expect it to use the existing instance of the material in an unmodified instance already exists in material library.

Steps:

• Create 3D project
• Add three spheres in the scene
• Drag brick material from content library to first sphere in navigator
• Drag brick material from content library to second sphere in navigator
• Drag brick material from content library to third sphere in 3d view

-> Expectation is that there is only one brick material node in content library after this and all spheres bind the same node.

If the brick material instance already in the material library has some modifications, in that case it should create another instance.