Filtering audio files by artist not working on Symbian

If I query for all of the audio files on device with DocumentGalleryModel QML plugin:

DocumentGalleryModel {
            rootType: DocumentGallery.Audio
            properties: [ "title", "artist", "albumTitle", "url" ]
            sortProperties: [ "title" ]
}

...I don't seem to be able to filter the result by artist:

filter: GalleryStartsWithFilter {
                id: songFilter
                property: "artist"
                value: "Frank Zappa"
            }

An empty list is returned, no matter what the filter value.
Filtering by e.g. title, albumTitle or albumArtist works fine, but using albumArtist on not a valid workaround as it is not often set in music files.

Attached is a sample app showing the problem (filters with artist or album starting with "A").

Reproduces at least on Symbian^3 (N8) with PS2 wk18, and also with Qt 4.7.3 + Mobility 1.1.3 installed from 1.1 SDK.