This is a difficult issue to describe so I have taken a screen shot of the problem.
To produce this unusual effect ........
Scan for issues that require using the scroll bar to view more than a full screen.
Click the arrow down button to keep scrolling down the list.
For each click of the down arrow it produces a feint grid line through each item.
It is interesting to note that this problem does not occur when the bar is dragged down to scroll through items.
<-- On the attachment you will see these feint lines from about half way down starting at the item ActiveDataInfo1.