Translucent User Interface materials do not have a thumbnail preview

Translucent User Interface materials do not have a thumbnail preview.

I do not see this issue with Translucent Surface materials.

REGRESSION:
No, this issue also occurs as far back as 4.17.2

1. Open UE4Editor.exe
2. Create a Third Person Blueprint project
3. Enable Show Engine Content in the Content Browser
4. Create a new Material
5. Add a Material Expression Constant 3 Vector node to the graph
6. Change the color and connect it to the Final Color pin
7. Search for the CameraActor_64x texture in the Engine Content
8. Drag the CameraActor_64x text into the new material graph
9. Connect the Alpha Channel pin to the Opacity pin
10. Apply and Save the material
11. Locate the new material in the Content Browser and hover the mouse over the thumbnail

RESULT:
The thumbnail is completely blank and does not have a preview

EXPECTED:
The thumbnail displays a camera shape