Index: /trunk/src/org/openstreetmap/josm/gui/layer/OsmDataLayer.java
===================================================================
--- /trunk/src/org/openstreetmap/josm/gui/layer/OsmDataLayer.java	(revision 11632)
+++ /trunk/src/org/openstreetmap/josm/gui/layer/OsmDataLayer.java	(revision 11633)
@@ -17,4 +17,5 @@
 import java.awt.event.ActionEvent;
 import java.awt.geom.Area;
+import java.awt.geom.Path2D;
 import java.awt.geom.Rectangle2D;
 import java.awt.image.BufferedImage;
@@ -412,13 +413,16 @@
             // over-grow it just to be sure
             b.grow(100, 100);
-            Area a = new Area(b);
-
-            // now successively subtract downloaded areas
+            Path2D p = new Path2D.Double();
+
+            // combine successively downloaded areas
             for (Bounds bounds : data.getDataSourceBounds()) {
                 if (bounds.isCollapsed()) {
                     continue;
                 }
-                a.subtract(mv.getState().getArea(bounds));
-            }
+                p.append(mv.getState().getArea(bounds), false);
+            }
+            // subtract combined areas
+            Area a = new Area(b);
+            a.subtract(new Area(p));
 
             // paint remainder