bootgrid将mulselect设成false，为什么选择框的type还是“checkbox"?

代码如下：

function test(){
    $("#examTable").bootgrid({
        ajax: true,
        ajaxSettings: {
            method:"POST",
            cache: false
        },
        post: function ()
        {
            var sortOrder = $("#examTable").bootgrid("getSortDictionary");
            var sortKey,sortName;
            ...
            $.each(sortOrder, function (name, value) {
                        sortKey = name;
            sortName = value;
            });
            return {
                "sort": sortKey,
                "sort_name": sortName,
                ...
            };
        },
        url: "/admin/exam/mgr_grid/",
        selection: true,
        multiSelect: false,
        navigation: 3,
        formatters: {
            "id": function(column, row)
            {
                return "";
            },
        }
    });
}

mulselext设置成false了，但是还是复选框。实际传递到后台的值是单选的值。截图如下：