Material Layers Relink Button Missing

The Relink button is missing (as are the Save Sibling and Save Child buttons) on Material Instances that use Material Attributes Layers in 5.5.

1. Create a Material that has Use Material Attributes set to true, and a Material Attributes Layers node connected in the graph
2. Create a Material Instance from the material
3. Open the Material Instance
4. Navigate to the Layer Parameters tab
5. Click the Unlink button
6. Observe that the Relink button does not appear. 
7. Additionally, observe that the Save Sibling and Save Child buttons are also missing