Index: src/org/openstreetmap/josm/gui/conflict/pair/relation/RelationMemberListMergeModel.java
===================================================================
--- src/org/openstreetmap/josm/gui/conflict/pair/relation/RelationMemberListMergeModel.java	(revision 6542)
+++ src/org/openstreetmap/josm/gui/conflict/pair/relation/RelationMemberListMergeModel.java	(working copy)
@@ -3,6 +3,8 @@
 
 import static org.openstreetmap.josm.tools.I18n.tr;
 
+import java.util.Collections;
+import java.util.Comparator;
 import java.util.List;
 import java.util.Map;
 
@@ -67,12 +69,25 @@
     public void populate(Relation my, Relation their, Map<PrimitiveId, PrimitiveId> mergedMap) {
         initPopulate(my, their, mergedMap);
 
+        final Comparator<RelationMember> relationMemberComparator = new Comparator<RelationMember>() {
+            @Override
+            public int compare(RelationMember o1, RelationMember o2) {
+                long x = o1.getUniqueId();
+                long y = o2.getUniqueId();
+                return (x < y ? -1 : ((x == y) ? 0 : 1));
+            }
+
+        };
         for (RelationMember n : my.getMembers()) {
             getMyEntries().add(n);
         }
+        Collections.sort(getMyEntries(), relationMemberComparator);
+
         for (RelationMember n : their.getMembers()) {
             getTheirEntries().add(n);
         }
+        Collections.sort(getTheirEntries(), relationMemberComparator);
+
         if (myAndTheirEntriesEqual()) {
             for (RelationMember m : getMyEntries()) {
                 getMergedEntries().add(cloneEntryForMergedList(m));