The ComboBox widget does not support setting BindTo and DataSource options simultaneously. In other words if Ajax binding is used it will ignore the data set with BindTo method.
In general, you can set the autoBind to false and define value and text options of the widget in order to prevent initial request. Please note that if the widget is not bound and its value method is called it will request the server. MVVM will call widget value method if the model property has value. You can check this code library, which shows how to use cascading widgets as an editor template.
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