MapCheck warnings when opening a map using landscape override material

1. Create a new level with OpenWorld map template
2. Create a material for landscape ( or Duplicate /Engine/Content/OpenWorldTemplate/M_ProcGrid )
3. Enter landscape mode
4. Select Manage > Select tool
5. Select some landscape components in level viewport
6. Set the material(step 2) to Override Material in detail pane
7. Exit landscape mode
8. Save the level
9. Reopen the level
10. Open Window > Message Log

Result:

We can find following warnings :

[landscape proxy path] : Fixed up invalid landscape material instances. Please re-save [hash name]. 

The landscape material is not modified and is not marked as dirty, so this warning can not be fixed.

Note :

The warnings does not show when using Nanite landscape.