Index: trunk/src/org/openstreetmap/josm/data/osm/DataSetMerger.java
===================================================================
--- trunk/src/org/openstreetmap/josm/data/osm/DataSetMerger.java	(revision 2752)
+++ trunk/src/org/openstreetmap/josm/data/osm/DataSetMerger.java	(revision 2753)
@@ -321,6 +321,8 @@
             objectsWithChildrenToMerge.add(source.getPrimitiveId());
         } else if (! target.isModified() && !source.isModified() && target.getVersion() == source.getVersion()) {
-            // both not modified. Keep mine
-            //
+            // both not modified. Merge nevertheless.
+            // This helps when updating "empty" relations, see #4295
+            target.mergeFrom(source);
+            objectsWithChildrenToMerge.add(source.getPrimitiveId());
         } else if (! target.isModified() && !source.isModified() && target.getVersion() < source.getVersion()) {
             // my not modified but other is newer. clone other onto mine.