Happens if the items had been set on-the-fly when opening the popup. To reproduce, use example in RT-22572 , add a button that null the selectedItem and run the following steps

- sanity check: click nullSelected - combo is cleared, as expected
- open popup
- select item from popup
- click nullSelected
- expected: combo cleared
- actual: combo still showing the last selected

Seem like a missing value update (selectedItem is null)

 Code snippet to insert:

        Button nullSelected = new Button("Null selectedItem");
        nullSelected.setOnAction(e -> {
            cb.getSelectionModel().select(null);
        });
        ... // add to view
        vbox.getChildren().addAll(tf, cb, nullSelected);