Screen Percentage does not behave correctly with SceneDepth Post Processing

This is a regression tested in //UE4/Release-4.27 CL18319896

Screen Percentage does not behave correctly with SceneDepth Post Processing. 

1. Create or open any project
2. Create a new Basic Level
3. Create a new Post Processing Material for Scene Depth name 'M_Post'
   1. Select the Result node change the Material Domain to Post Process
   2. Create a Scene Depth node
   3. Connect it to a Multiply node
   4. Set B in the Multiply node to 0.0001
   5. Connect the output pin of the Multiply node to the Emissive input pin of the Result node
   6. Compile, save, and close the material
4. Add a Post Processing Volume to the level
   1. Enable Infinite Extent (Unbound)
   2. Add an element to the Post Process Material array
   3. Set that Element to Asset Reference
   4. Set this value to 'M_Post'
5. Under Viewport Options set Screen Percentage to 50

Expected Results:
The Screen Percentage is set to 50, and fills the viewport

Actual Results:
The Screen Percentage is set to 50, but the viewport displays both 100 and 50