The difference is in List properties that also have a setter. Take example from RT-17714.

The following FXML will call the handle method, as the items property in ListView contains the list constructed in the FXML:
<?import java.lang.*?>
<?import java.util.*?>
<?import javafx.collections.FXCollections?>
<?import javafx.scene.control.ListView?>

<ListView fx:controller="collectioneventshandler.SampleController"
                   xmlns:fx="http://javafx.com/fxml">
    <items>
    <FXCollections fx:factory="observableArrayList"
                   onChange="#handleListChangeEvent">
        <String fx:value="ABC"/>
    </FXCollections>
    </items>
</ListView>

However, using the default property will just add the list content to the items property:
<?import java.lang.*?>
<?import java.util.*?>
<?import javafx.collections.FXCollections?>
<?import javafx.scene.control.ListView?>

<ListView fx:controller="collectioneventshandler.SampleController"
                   xmlns:fx="http://javafx.com/fxml">
    <FXCollections fx:factory="observableArrayList"
                   onChange="#handleListChangeEvent">
        <String fx:value="ABC"/>
    </FXCollections>
</ListView>