sorting QML DocumentGalleryModel according to filepath does not work

I am trying to sort the QML DocumentGalleryModel according to filepath so that its sorted in the ascending order of file path. Here is my code

import QtQuick 1.0
import QtMobility.gallery 1.1
DocumentGalleryModel
{
rootType: DocumentGallery.Audio
properties: ["filePath","url","fileName","path","fileExtension","albumTitle","artist"]
sortProperties: [ "filePath" ]
}

But when the results are viewed, the sorting is not done. The items in the model are displayed randomly without any order. However if I try to sort with albumTitle, the returned results are perfectly sorted