We have noticed that if viewing the backlog items on the Kanban board view that the right vertical scroll bar disappears once you also open an issue. If you view the backlog of issues the vertical scroll bar is visible. But as soon as you open up an individual issue to appear on the right, the vertical scroll bar disappears.
Functionality still exists, but the slider bar is hidden until you click down in the scroll bar area.
Yes, it is a minor annoyance...but I have picky customers. 
