How to reproduce:
1. Open
2. Create a new project
3. Create an empty GameObject
4. Attach MeshRenderer and SkinnedMeshRenderer components
5. Try to expand 'Material' and 'lighting' groups clicking on their labels

Expected result: Both groups open in the same way
Actual result: 'Materials' group opens while clicking on a label when 'lighting' group won't

Reproducible with - 5.6.0f1, 5.6.1f1, 5.6.4p3, 2017.1.0a1, 2017.1.2p3, 2017.2.0a1, 2017.2.0p2, 2017.3.0a1, 2017.3.0b10, 2018.1.0a1, 2018.1.0a5
Could not test:
5.6.0a1, 5.6.0b1 (MeshRenderer components doesn't have lighting group yet)

Fixed and verified in 2018.2.0a3