I have not used Swing in ages and now that I've had to pick it up again I've encountered the same slight yet annoying problem on both Windows 8 and Xubuntu 14.04.
When I resize a JFrame by dragging one of it's borders outwards with the mouse-cursor, the windows content-pane seems to lag behind the frame itself, thus creating a black border of varying size in the direction in which the JFrame is enlarged. As stated this happens on different machines and operating systems, It's definitely not an implementation problem; Netbeans exhibits this behavior as well. I have Java version 1.8.0_45 installed in both cases.
Does anybody else experience this?