Scroll Bar does not Stay "Anchored" to Bottom While Data Generates in Window

The scrollbar no longer remains anchored to the bottom of the Output Log while more lines are propagated during the packaging process/

Regression: this does not occur in previous versions of the Engine:
Is working in Binary Release UE4.11.2 CL: 2946394
Is no longer working in Binary Release UE4.12.0 CL: 2992821

1. Open a Blank Blueprint Project
2. Package project > Windows > 32 bit or 64 bit
3. Show Output Log
4. Move scroll bar to bottom while data propagates in the window
   RESULT: as more data is added, the scrollbar does not remain "anchored" at the bottom
   EXPECTED: The scrollbar remains anchored to the bottom no matter how many more lines are propagated during the packaging process