Slate Widget STileView Scrolling Mouse Wheel Lock

When using the mouse wheel to scroll nested scroll boxes, scrolling up no longer works once the inner tile view has been scrolled to the top.

Regression:
Yes, this behavior does not occur in 4.16.3 (CL 3561208)

1. Download attached project
2. Open the editor and launch the Substance Source window. This can be done by clicking on the Substance button which has been added to the main editor toolbar.
3. Select the Ceramic category
4. Scroll to the bottom of this window using the mouse wheel.
5. Scroll to the top of the window using the mouse wheel.

Result:
The window does not scroll back to the top,