Using 1.75.7 -- If a system has enough staves to require a vertical scroll-bar and you then layer enough of them for the system to fit within the window the scroll-bar is not removed, but the space it occupies changes to dark gray and black, until you scroll horizontally, at which time the display returns to normal. This does not happen when the need for the scroll-bar ends due to change in size of the staves.
I am not certain that this always happens, but I know that it does often.