Material Instance Parameter Values Reset When Renamed

Per Licensee:

We would like to change some of their parameter names, however when renaming a parameter, its value in all of the corresponding material instances resets to the base material default value.

This is a regression. This does not occur in 4.17. This does not occur if the base material does not include a material function.

1. Open attached Project
2. Open Mat_Test2 and Mat_Test2_Inst
3. Notice that in Mat_Test2_Inst the Vector Parameter Value for 'BaseColor321' has been overridden and changed to a red color.
4. In Mat_Test2 select Parameter 'BaseColor321' and change name (I changed to 'BaseColor123' for screenshots), then save material.

Result: Mat_Test2_Inst the Vector Parameter Value for 'BaseColor123' has reset to default value of base material.
Expected: Changing parameter name doesn't change parameter values.