quick fix fix

src/ui/view/GUI.java

@@ -1990,7 +1990,7 @@ public class GUI<E> implements CategoryListener {
 		MouseAdapter focusCanvas = new MouseAdapter() {
 			@Override
 			public void mouseExited(MouseEvent e) {
-				canvas.requestFocus();
+				contentPane.requestFocus();
 			}
 		};