scroll bars keep scrolling

I've had this problem for years, but it hasn't irritated me enough until today. Whenever I open up iTunes and want to look for a song or album that is below what is showing, I'll click on the scroll bar on the right and press the mouse button until I get in the general area of what I'm searching for. Most of the time, that will be the end of it. One click, one scrolling page.

But, every so often, I will click on an empty space in the scroll bar area and it will start scrolling until it reaches the bottom or the mouse pointer is moved away from the scroll bar. Move the pointer away, the scrolling stops. Bring the pointer back to the scroll bar, and it continues to scroll. Take it away, and it stops. One click, multiple scrolling pages.

This only happens on iTunes and nowhere else. I'm using a Windows laptop with a built-in mouse pad with Synaptics software, running Windows 10 currently, but this problem also appeared on my previous OS Windows 7. Any help would be very much appreciated.