Static Mesh Component variable defaults cannot be set in the Details panel

Static Mesh Component variable defaults cannot be set in the Details panel. No options are available in the dropdown, even if the Blueprint already has StaticMesh components assigned.

Reproduced in 4.7.5 binary and Main (//depot/UE4/Promotable-CL-2507843)

1. Open any project
2. Create a new Actor Blueprint
3. Add a Static Mesh component
4. Assign a static mesh to the component
5. Add a Static Mesh Component variable
6. Compile
7. Click the drop-down menu in the Details for the variable to select a Static Mesh Component

Result:
The list is empty.

Expected:
A list of Static Mesh Components within the Blueprint.