Index: /trunk/src/org/openstreetmap/josm/data/osm/visitor/MergeVisitor.java
===================================================================
--- /trunk/src/org/openstreetmap/josm/data/osm/visitor/MergeVisitor.java	(revision 489)
+++ /trunk/src/org/openstreetmap/josm/data/osm/visitor/MergeVisitor.java	(revision 490)
@@ -140,5 +140,5 @@
 
 	private static <P extends OsmPrimitive> boolean match(P p1, P p2) {
-		if (p1.id == 0 || p2.id == 0) {
+		if ((p1.id == 0 || p2.id == 0) && !p1.incomplete && !p2.incomplete) {
 			return realMatch(p1, p2);
 		}