Index: trunk/test/unit/org/openstreetmap/josm/data/osm/DataSetTest.java
===================================================================
--- trunk/test/unit/org/openstreetmap/josm/data/osm/DataSetTest.java	(revision 16202)
+++ trunk/test/unit/org/openstreetmap/josm/data/osm/DataSetTest.java	(revision 16212)
@@ -316,3 +316,27 @@
         new DataSet().mergeFrom(ds);
     }
+
+    /**
+     * Checks that a read-only dataset can be cloned.
+     */
+    @Test
+    public void testCloneReadOnly() {
+        DataSet ds = new DataSet();
+        Node n1 = new Node(LatLon.SOUTH_POLE);
+        Node n2 = new Node(LatLon.NORTH_POLE);
+        ds.addPrimitive(n1);
+        ds.addPrimitive(n2);
+        Way w = new Way();
+        w.setNodes(Arrays.asList(n1, n2));
+        ds.addPrimitive(w);
+        Relation r = new Relation();
+        r.setMembers(Arrays.asList(new RelationMember(null, w)));
+        ds.addPrimitive(r);
+        ds.lock();
+
+        DataSet copy = new DataSet(ds);
+
+        assertEquals(4, copy.allPrimitives().size());
+        assertTrue(copy.isLocked());
+    }
 }