How to reproduce:

1. load the SampleScene
2. look at the face in the scene
3. move the smile blend shape up and down
4. notice the broken normals
5. find the fbx under assets/faces
6. expand the blendshapeTest_n face asset
7. right click on the mesh_body subasset
8. select 'generate mesh with fixed normals'
9. see a new asset is produced
10. select the face in the scene
11. drag this fixed mesh asset onto face's mesh reference in the skinned mesh renderer
12. change the smile blend shape value
13. see that the blend shape is corrupted

Result: Blend shape is corrupted
Expected: Blend shape should work

14. save the scene
15. right click on assets and select 'reimport all'
16. wait for editor to restart
17. select the face in the scene
18. change the smile blendshape value
19. see that the blendshape now works correctly

Result: mesh blend shapes saved in this script are broken without a complete library re-import
Expected result: the mesh blendshapes should not require a complete re-import

First reproduced in 2018.3.9f1
Not reproducible in 2018.3.8f1