Material Function Instances do not show up in the Material Function Call node

This is not a regression. Tested in //UE5/Release-5.1 CL23901901.

The Material Function Instance can be dragged and dropped into the Material Function Call.

1. Create or open any project
2. Create a Material Function by right clicking in the content browser then selecting Material > Material Function
3. In the Material Graph create a Make Material Attributes then connect its output pin to the Output Results
4. Create a Texture Sample Parameter 2D then connect the RGB output pin to the Base Color input pin of the Make Material Attributes node
5. Apply, save, and close the Material Editor
6. In the Content Browser right click the Material Function then select Create Function Instance
7. Create a new Material
8. In the Material Graph create a Material Function Call
9. Select the Material Function Call then in the Details Panel select the Material Function drop down
10. Search for the Material Function Instance created in step 6

Expected Results:
The Material Function and the Material Function Instance both appear in the list.

Actual Results:
The Material Function appears in the list, but the Material Function Instance does not.