If “Support Material Layers” is enabled (Experimental features in ‘Project settings’), every time you uncheck an overridden parameter in a material instance the value of that parameter will reset to its parent’s default value.
This makes the whole system very frustrating to use, since you are constantly losing your parameter values.
1 - Create a new project
2 - Enable ‘support Material Layers’ in project settings
3- Restart editor
4 - Create a new material with a parameter
5 - Create a material instance of said new material
6 - Check the parameter override and change the value
7 - Uncheck the parameter override. The value will reset to its default value.
This doesn’t happen if “Support Material Layers” is disabled. The value merely turns gray, indicating it isn’t being used.