ScrollPane displays grayed out areas when the heigth of the components
added to the ScrollPane is smaller but so close to the heigth of the ScrollPane, and scrollbars are not needed.

In other words ScrollPane shows grayed out area in place of scroll
bars when ScrollBar is not needed, and the heigth of the components inside
the ScrollPane is very close to the heighth of the ScrollPane.

In other words, the area where scrollbars would be (if needed) still showing a gray box when no scroll bar is needed.

Attached is a test case (paneTest.java), compile the application and run it.
Then experiment by resizing the frame using the mouse. When the ScrollPane is
a little larger than the List, you'll see grayed out area's where scrollbars
would have been if they were needed.

Also please see related bug 4097589.