It is easier to demonstrate than explain :)

Expected behavior: Click and drag the scrollbar on the right, the screen
scrolls.As long as you have the mouse pressed, the scrolling continues,
even if the mouse is outside the scroll bar.

Bug: Click and drag on the scrollbar, but without letting go off the mouse,
move the mouse into the horizontal menu bar/toolbar/search bars area
(towards the foot)... Happens often when you are scrolling up and you reach
the top of the page. Let go of the mouse. The screen continues to scroll
with the mouse up or down, eventhough mouse is not pressed.

Thank you for listening!

krishna