Destructible mesh: New generated Fracture Materials don't have any responded surfaces

I think this issue was happen since 4.18 in which version Apex Destructible was move to Plugin

• Enable Apex Destructible plugin and launch editor
• Use this mesh (StaticMesh'/Engine/BasicShapes/Sphere.Sphere') to create a destructible mesh
• Open the newly created destructible mesh and Do Fracture Mesh by click the button on the top tool bar
• In Destructible settings, see a new extra material slot created which should be used on the Fracture surfaces 
• Change the material in the that slot, the fracture surface don't change. Looks like the fracture surface is always using the material same as rest of the models

Expectation: Fracture surfaces should be apply with fracture Material