This is a classic HTML/JS dragging bug with every scrollbar in the new UI. You have to handle focus/blur and other layers correctly. This bug has been present ever since I've used the UI. I'm surprised it's still there. 1. Click to drag on scrollbar 2. Scroll up/down 3. While scrolling move your cursor off the scrollbar: scrolling stops, and you can release the mouse button and move back to the scrollbar and it will then start scrolling along with your cursor even though you don't have your mouse button clicked Expected behaviorur: See Windows scrollbars where you don't have to have your cursor on the scrollbar you can move side to side say 60pixels (at least in Firefox) and it will still scroll. Point being, just moving your cursor off the scrollbar shouldn't prevent it from scrolling. It requires the user to be too exact with their mouse movement to require them to be on the scrollbar all the time while they're scrolling. It shouldn't also lose track of if you have the button clicked while off the scrollbar.
