Index: trunk/test/unit/org/openstreetmap/josm/io/GeoJSONReaderTest.java
===================================================================
--- trunk/test/unit/org/openstreetmap/josm/io/GeoJSONReaderTest.java	(revision 18006)
+++ trunk/test/unit/org/openstreetmap/josm/io/GeoJSONReaderTest.java	(revision 18007)
@@ -217,4 +217,23 @@
 
     /**
+     * Non-regression test for <a href="https://josm.openstreetmap.de/ticket/21044">Bug #21044</a>.
+     * @throws Exception in case of error
+     */
+    @Test
+    void testTicket21044Duplicates() throws Exception {
+        try (InputStream in = TestUtils.getRegressionDataStream(21044, "test.geojson")) {
+            final List<OsmPrimitive> primitives = new ArrayList<>(
+                    new GeoJSONReader().doParseDataSet(in, null).getPrimitives(it -> true));
+            assertEquals(1, primitives.size());
+            OsmPrimitive primitive = primitives.get(0);
+            assertTrue(primitive instanceof Node);
+            Node n = (Node) primitive;
+            assertNull(n.get("addr:building"));
+            assertEquals("06883", n.get("addr:postcode"));
+            assertEquals("22;26", n.get("addr:housenumber"));
+        }
+    }
+
+    /**
      * Tests error reporting for an invalid FeatureCollection
      * @throws Exception in case of error
@@ -229,4 +248,3 @@
         }
     }
-
 }