Index: trunk/src/org/openstreetmap/josm/actions/CreateMultipolygonAction.java
===================================================================
--- trunk/src/org/openstreetmap/josm/actions/CreateMultipolygonAction.java	(revision 17210)
+++ trunk/src/org/openstreetmap/josm/actions/CreateMultipolygonAction.java	(revision 17214)
@@ -492,4 +492,6 @@
                 }
                 commands.add(new ChangeCommand(ds, relation, r2));
+            } else {
+                r2.setMembers(null); // see #19885
             }
         }