Index: trunk/src/org/openstreetmap/josm/gui/dialogs/relation/GenericRelationEditor.java
===================================================================
--- trunk/src/org/openstreetmap/josm/gui/dialogs/relation/GenericRelationEditor.java	(revision 3919)
+++ trunk/src/org/openstreetmap/josm/gui/dialogs/relation/GenericRelationEditor.java	(revision 3920)
@@ -1545,6 +1545,9 @@
 
                 toAdd = filterConfirmedPrimitives(toAdd);
-                memberTableModel.addMembersAfterIdx(toAdd, memberTableModel
-                        .getSelectionModel().getMaxSelectionIndex());
+                int index = memberTableModel.getSelectionModel().getMaxSelectionIndex();
+                if (index == -1) {
+                    index = memberTableModel.getRowCount() - 1;
+                }
+                memberTableModel.addMembersAfterIdx(toAdd, index);
 
                 tfRole.requestFocusInWindow();