Member sidebar Duplicate ignores multi-selection

When several items are selected in the code editor's member sidebar, the Duplicate command only duplicates one of them.

Steps:

1. Create a project and add three methods to a class or module.
2. Select all three methods in the member sidebar.
3. Right-click and choose Duplicate (or press the Duplicate shortcut).

Only one method is duplicated. The rest of the selection is ignored. The same happens with notes, and multi-selecting controls in the sidebar and pressing the Duplicate shortcut does nothing at all.

Expected: every selected item is duplicated, matching Cut, Copy, and Delete, which already act on the whole selection.