Kendo UI Filter with field bound to DropDowList : ExpressionPreview doesn't display text value.

[Patrice Cote]

Hi! I have a Kendo UI Filter with a column bound with a DropDownList. Everything works fine, except the ExpressionPreview gives me "[object Object]". I read that I could use the PreviewFormat, but I have no clue about how that works if it's not for numeric values. Your documentation is very thin about the subject. Can you tell me how could I see the property set as DataTextField in the preview? Or at least the DataValueField.
My razor looks like :
 @(Html.Kendo().Filter<OrderSearchBindingModel>()
.Name("filter")
.ApplyButton()
.ExpressionPreview()
.MainLogic(FilterCompositionLogicalOperator.Or).Fields(f =>
  {

      f.Add(x => x.Symbole).Label("My values list").Operators(c => c.String(x => 
                          x..Contains("Contient")).EditorTemplateHandler("getSymboleList")
}).DataSource("source"))
 
And the script containing the dropdown logic is like this :

.kendoDropDownList({
                dataTextField: "SymboleDisplayName",
                dataValueField: "Symbole",
                dataSource: {
                    type: "json",
                    transport: {
                        read: "https://myodataurl.com/symbols/getSymbols"
                    },
		    schema: {
			data: "value"
		    }
                }
            });

 
Note that my datasource is an OData query, so I defined a schema with data: "value" in my kendo.data.DataSource object as well as type: "json". The type is aslo specified in the transport.read preperties datatype: "json"