UPDATE:
By design: Scene formats should never "autochange" - Opening a scene and saving it again should not change what is stored already.

Steps to reproduce:

1. Open attached project
2. Open scene "Main"
3. In Hierarchy select "Hf_Female_Test" and expand it
4. Select any "Base_LOD" child and select it
5. Actual result - In Debug Inspector, notice that Blend Shape Weight list is empty

Expected result - Blend Shape Weight list holds weight for every blend shape that mesh has.

Bug introduced in 5.0