Reproducible with following unit test that I added to the ComboBoxTest class:

@Test public void test_jdk_8160493() {
    AtomicInteger count = new AtomicInteger();
    comboBox.valueProperty().addListener(o -> count.incrementAndGet());
    assertEquals(0, count.get());

    comboBox.getItems().addAll("Apple", "Orange", "Banana");
    sm.select(1);
    assertTrue(sm.isSelected(1));
    assertEquals(1, count.get());
    assertEquals("Orange", comboBox.getValue());

    comboBox.setValue("New Value");
    assertEquals(2, count.get());
    assertEquals("New Value", comboBox.getValue());
}