Comment 3 for bug 1014208

By looking at Ambiance (in package light-themes), looks like there are a lot of files related to sliders (in gtk-3.0/assets):

slider_backdrop.png slider_vertical_backdrop.png
slider_insensitive_backdrop.png slider_vertical_insensitive_backdrop.png
slider_insensitive.png slider_vertical_insensitive.png
slider_prelight.png slider_vertical.png
slider_prelight_vertical.png

The most important to me is slider_prelight.png. I think the reason that it's "disappearing" after it gets scrolled over is because it can't find the image for it, so it becomes a box of one of Salience's color.