Kendo Dropdownlist: Grouping data causes undefined

Kendo Dropdownlist: Grouping data causes undefined

Im trying to use an existing data file to populate a kendo drop down
list.The field im interested in populating my drop down list is the "make"
field which basically displays a list or car manufacturers.
this works fine...
var makes = $("#makes").kendoDropDownList({
optionLabel: "Select make...",
dataTextField: "make",
dataValueField: "make",
dataSource: {
transport: {
read: {
dataType: "jsonp",
url: "data.php",
}
},
schema: {
data: "data"
}
}
}).data("kendoDropDownList");
However there are many makes repeated as its a list of car specs so i want
to be able to group the data by make to hide the repetitions. As soon as i
add this line the dropdowlist options become undefined.
group: { field: "make" }
Code after i added group
var makes = $("#makes").kendoDropDownList({
optionLabel: "Select make...",
dataTextField: "make",
dataValueField: "make",
dataSource: {
transport: {
read: {
dataType: "jsonp",
url: "data.php",
}
},
schema: {
data: "data"
},
group: { field: "make" }
}
}).data("kendoDropDownList");
Any idea's guys
thanks