Default Values of Parameters from Material Function not saving in Material Instances

A Parameter set in a Material Function cannot be reset to a default value in a Material Instance.

Reproduced in 4.7p7 CL-2440994 and Main Promotable-CL-2444381

1. Open QAGame Editor
2. Create a New Material Function named MF_1
3. Add a Vector Parameter called Color connected to the Output Results
4. Create a New Material named M_Layer
5. Add MF_1 to M_Layer connected to Base Color
6. Create a New Material Instance from M_Layer called MI_Layered
7. In MI_Layered, change the value of Color
8. Try to reset to default with the yellow arrow

RESULTS: Default Value is not restored

EXPECTED: Default Value returns to the MI