How to reproduce:
1. Open the attached project
2. Open and play TestScene scene
3. Select the Content in the hierarchy window (this is just so that you can see whether the content actually moves in the scene view by watching the recttransform borders move)
4. Click the scrollrect in the gameview and try to scroll down using a scrollwheel. (this works just fine)
5. Now drag the scrollbar all the way down so that you are viewing the bottom of the content
6. Try to scroll up again using the scrollwheel

Actual: The content doesn't move up
Expected: The content moves up

7. Change content height to 500000 or uncomment line 69 of the ScrollRectTest.cs script and repeat all previous steps. Notice how it now does scroll back up.