Adding an entry to arrays within Details Panels automatically collapses expanded entries

Adding an element to an array in the Material Editor automatically collapses all expanded elements in the array.
I've successfully reproduced this issue with the following nodes:

• LandscapeGrassOutput
• LandscapeLayerBlend

I'm able to reproduce this issue as far back as the live 4.20.3 Binary (CL 4377374). I cannot reproduce in the live 4.19.2 Binary (CL 4033788).

It is therefore marked as a regression.

1. Open any project in UE4Editor
2. Create a a new Material
3. Open the newly-created Material
4. Right-click within the graph
5. Search for and select a LandscapeGrassOutput node
6. In the Material Editor Details Panel, expand Element 0
7. In the Material Editor Details Panel, add a new element to the Grass Types array

Result:
The Grass Types array collapses all elements when a new element is addd

Expected Result:
Expanded elements are not collapsed when a new element is added