Why Vaadin does not select rows on right click in Grid?

Looking at our source, we do:

contextMenu.addGridBodyContextMenuListener(this)

public void onContextMenuOpen(GridContextMenuOpenEvent event) {

    // If clicking outside of current selection, set selection to clicked row.
    Object itemId = event.getItemId();
    boolean rowIsSelected = itemId!=null && grid.isSelected(itemId);
    ...
    // optionally rebuild menu based on selection

}