After "Reimport All" materials, prefabs models lost lightning in icons.
If project was reopened or "Reimport" option is used, lightning is present in icons.

To reproduce:
1. Create a material. Add some albedo.
2. In project tab press Reimport all.
3. Select created Material.

Actual result: Icon of material in Project tab is shaded.
Expected result: Assets are reimported without changes.
Workaround: Press Reimport. Materials/models/prefabs icons would look as expected.

Reproduces in 5.5, 5.4.x, .. 5.0.4.