Index: src/org/openstreetmap/josm/data/osm/DataSetMerger.java
===================================================================
--- src/org/openstreetmap/josm/data/osm/DataSetMerger.java	(revision 4727)
+++ src/org/openstreetmap/josm/data/osm/DataSetMerger.java	(working copy)
@@ -178,6 +178,9 @@
 
                 List<OsmPrimitive> referrers = target.getReferrers();
                 if (referrers.isEmpty()) {
+                    if (target instanceof Way) { // fix #7194
+                        ((Way) target).setNodes(null);
+                    }
                     target.setDeleted(true);
                     target.mergeFrom(source);
                     it.remove();