Telerik.Web.UI.GridMobileGroupView.prototype._handleCloseUp = function (e) {
    this._groupFieldNames.splice(index, 1);
    this._initPositions();

    var $target = $(e.target);
    var $parentGroupItem = $target.parents(".rgColumnItem");
    this._$groupExpressions = this.get_$element().find(".rgColumnItem");
    var index = this._$groupExpressions.index($parentGroupItem);
    var groupFieldsMap = {};
    $(this._dragData).each(function (index, item) {
        var elem = item.$element;
        groupFieldsMap[elem.data("groupFieldName")] = elem[0];
    });
    $parentGroupItem.remove();
    for (var groupField in groupFieldsMap) {
        if (groupFieldsMap[groupField] == $parentGroupItem[0]) {

            /** Original */
            //this.get_owner().fireCommand("UnGroupByColumn", groupField);

            /** Override */
            var columnUniqueName = this.get_owner().get_columns().filter(col => col._data.Groupable && col.get_dataField() == groupField)[0].get_uniqueName();
            this.get_owner().fireCommand("UnGroupByColumn", columnUniqueName);

            break;
        }
    }
    this._groupFieldNames.splice(index, 1);
    this._initPositions();
}