Index: /trunk/src/org/openstreetmap/josm/gui/io/DownloadPrimitivesWithReferrersTask.java
===================================================================
--- /trunk/src/org/openstreetmap/josm/gui/io/DownloadPrimitivesWithReferrersTask.java	(revision 13533)
+++ /trunk/src/org/openstreetmap/josm/gui/io/DownloadPrimitivesWithReferrersTask.java	(revision 13534)
@@ -8,4 +8,5 @@
 import java.awt.GridBagLayout;
 import java.io.IOException;
+import java.text.MessageFormat;
 import java.util.ArrayList;
 import java.util.HashSet;
@@ -76,4 +77,11 @@
         this.full = full;
         this.newLayer = newLayer;
+        // Check we don't try to download new primitives
+        for (PrimitiveId primitiveId : ids) {
+            if (primitiveId.isNew()) {
+                throw new IllegalArgumentException(MessageFormat.format(
+                        "Cannot download new primitives (ID {0})", primitiveId.getUniqueId()));
+            }
+        }
         // All downloaded primitives are put in a tmpLayer
         tmpLayer = new OsmDataLayer(new DataSet(), newLayerName != null ? newLayerName : OsmDataLayer.createNewName(), null);