Reimporting a static mesh with modified material LODs does not update the materials correctly

In Main the cube Section0 LOD material is replaced with the DefaultGrid material which is also not expected.

This appears to be a regression from 4.15 based on the test execution history.

1. Import Import_Sections_List_LOD.FBX from \Engine\Content\NotForLicensees\QA\Import_Test_Assets\FBX\StaticMesh
2. Check "Import Mesh LODs" and make sure "Import Materials" and "Import Textures" are also checked
3. Click Import
4. Drag an instance of the static mesh into the viewport and hit F to focus it (LOD0 should be displayed)
5. Open the imported static mesh in the editor
6. Change LOD0's Section 0 Material Slot from Cyan to Lime
7. Click the ellipsis in Import Settings next to Source File
8. In the dialogue that appears select the Import_Sections_List_LOD_Reimport FBX file and click Open
9. Click Save in the Static Mesh Editor, then close it
10. Find the Import_Sections_List_LOD Static Mesh in the Content Browser, then right click it and select Reimport

Result: Cube in the viewport remains a Lime color
Expected: Cube in the viewport reverts to Cyan