Index: trunk/src/org/openstreetmap/josm/actions/CreateMultipolygonAction.java
===================================================================
--- trunk/src/org/openstreetmap/josm/actions/CreateMultipolygonAction.java	(revision 16555)
+++ trunk/src/org/openstreetmap/josm/actions/CreateMultipolygonAction.java	(revision 16557)
@@ -115,7 +115,9 @@
             // to avoid EDT violations
             SwingUtilities.invokeLater(() -> {
-                    UndoRedoHandler.getInstance().add(command);
+                UndoRedoHandler.getInstance().add(command);
                 final Relation relation = (Relation) MainApplication.getLayerManager().getEditDataSet()
                         .getPrimitiveById(commandAndRelation.b);
+                if (relation == null || relation.getDataSet() == null)
+                    return; // should not happen
 
                 // Use 'SwingUtilities.invokeLater' to make sure the relationListDialog
@@ -127,4 +129,6 @@
                     if (Config.getPref().getBoolean("multipoly.show-relation-editor", false)) {
                         //Open relation edit window, if set up in preferences
+                        // see #19346 un-select updated multipolygon
+                        MainApplication.getLayerManager().getEditDataSet().clearSelection(relation);
                         RelationEditor editor = RelationEditor
                                 .getEditor(MainApplication.getLayerManager().getEditLayer(), relation, null);
@@ -133,4 +137,8 @@
                     } else {
                         MainApplication.getLayerManager().getEditLayer().setRecentRelation(relation);
+                        if (multipolygonRelation == null) {
+                            // see #19346 select new multipolygon
+                            MainApplication.getLayerManager().getEditDataSet().setSelected(relation);
+                        }
                     }
                 });