title: Graphics are erased from Canvas when scrolling in ScrollPane
body: <p>I have a <code>JFrame</code> that contains 4 instances of <code>ScrollPane</code>, each with its own <code>Canvas</code> and <code>BufferStrategy</code>.  When my drawing first takes place everything works as expected, but when I scroll in <code>ScrollPane</code> the graphics that are scrolled out of view are erased when I scroll them back into view.</p>