Index: /trunk/src/org/openstreetmap/josm/io/OsmReader.java
===================================================================
--- /trunk/src/org/openstreetmap/josm/io/OsmReader.java	(revision 2397)
+++ /trunk/src/org/openstreetmap/josm/io/OsmReader.java	(revision 2398)
@@ -518,4 +518,13 @@
                     }
                     ds.addPrimitive(primitive);
+
+                    if (rm.type.equals("node")) {
+                        externalIdMap.put("n" + rm.id, primitive);
+                    } else if (rm.type.equals("way")) {
+                        externalIdMap.put("w" + rm.id, primitive);
+                    } else if (rm.type.equals("relation")) {
+                        externalIdMap.put("r" + rm.id, primitive);
+                    }
+
                 }
                 relationMembers.add(new RelationMember(rm.role, primitive));