Index: src/org/openstreetmap/josm/gui/dialogs/relation/MemberTableModel.java
===================================================================
--- src/org/openstreetmap/josm/gui/dialogs/relation/MemberTableModel.java	(revision 15234)
+++ src/org/openstreetmap/josm/gui/dialogs/relation/MemberTableModel.java	(working copy)
@@ -279,7 +279,7 @@
         selectionModel.clearSelection();
         BitSet selected = new BitSet();
         for (int row : selectedRows) {
-            row--;
+            row += delta;
             selected.set(row);
         }
         addToSelectedMembers(selected);
@@ -532,6 +532,8 @@
     public Collection<RelationMember> getSelectedMembers() {
         List<RelationMember> selectedMembers = new ArrayList<>();
         for (int i : getSelectedIndices()) {
+            /* This is required due to using the method for Java 11 */
+            if (i > members.size() - 1) continue;
             selectedMembers.add(members.get(i));
         }
         return selectedMembers;