combo-box always opens up

In Vaadin demo combo-box opens up only if there isn't enough space to open down. But in my case it opens always up.

How to fix it? (can it happens because of changes to style, that we made?)

public class LocationSelector extends CssLayout {
    public LocationSelector() {
        ComboBox locationBox = new ComboBox();
        locationBox.addItems("Long Beach, CA", "Washington, DC", "Other");
        locationBox.setNullSelectionAllowed(false);
        locationBox.setNewItemsAllowed(false);
        locationBox.setInputPrompt("Select your city");
        locationBox.setStyleName("locationBox");
        locationBox.setPageLength(1000);
        this.addComponent(locationBox, "locationBox");
    }
}