I've created this plunk[1] to show the bug.
Scroll down while keeping your mouse inside the grid, keep your mouse in grid and, now try to scroll up.
This bug doesn't seem to appear in the 3.0.0-rc.19 release.
Is there a solution to this in the latest 3.0.0-rc.20 release?
[1] http://plnkr.co/edit/ke8jCXG7qsOzWRqOsrw1?p=preview