To reproduce:
1. Create a new project
2. Create a Material in Project view using context menu
3. Select something else (like Main camera in the scene view, or another asset in the project view)
4. Select the Material
Expected result: Inspector shows the material and you can change it, also you're able to add the Material to gameobjects
Actual result: Inspector is blank and you cannot add the material to gameObjects.

Note: after opening a project with such a Material in 5.0.1p2 and rebuilding (Yes, I know that downgrading projects is not supported), the Material created previously loaded up just fine and can be added to gameObjects.