src/java.desktop/share/classes/javax/swing/plaf/basic/BasicComboPopup.java

*** 1047,1056 ****
--- 1047,1058 ----
          public void itemStateChanged( ItemEvent e ) {
              if (e.getStateChange() == ItemEvent.SELECTED) {
                  @SuppressWarnings("unchecked")
                  JComboBox<Object> comboBox = (JComboBox)e.getSource();
                  setListSelection(comboBox.getSelectedIndex());
+             } else {
+                 setListSelection(-1);
              }
          }
  
          //
          // MouseWheelListener