I use amarok v. 2.8.0 compiled on Sep 25 2013, with Ubuntu 14.04 LTS, in a french environment
I have an mp3 version of a chinese album with the metadata below.
_________
titre/title : 怕
artiste/artist : 陳冠希 - Edison
compositeur/composer : empty
artiste de l'album/album artist: Edison
album: Please steal this album
Genre: Pop
Année/year: 2004
numéro de la piste/track number: 6
numéro du disque/disc number: 1
battements par minutes/beats per minutes: empty
commentaire/comment: 0
track location: /media/ferelden/musique5/gr52/06 怕.mp3
no lyrics/no cover album
_________
I open the metadata editor for this single file
I copy the artist : "陳冠希 - Edison" and replace the field album artist with "陳冠希 - Edison"
The "save and close" button becomes available.
I click on it. I don't modify any other fields.
I see absolutely no change to my playlist ordering by Album, I which I have first 5 tracks for the album artist "Edison", then 10 tracks for the album artist "陳冠希 - Edison". I expect the track to move down and meet the other tracks for the album artist "陳冠希 - Edison". 

I delete my playlist and my search for the album name.
I update collection in tools/"Mettre à jour ma collection" (4th option out of 5)
I search again for the album, and drag all my tracks in the empty playlist panel.
The track "怕" is still with the first 5 songs that have the album artist "Edison"
When I open the metadata editor, no changes were made to the song. The album artist is still "Edison".

Workaround:
I add a space (" ") at the end of track name and change the album artist field.
I click on button"save and close".
Hourray : the file is now with the tracks that have the album artist "陳冠希 - Edison"
When I open the metadata editor for the file, the field has the wanted value.
Don't forget to revert the track name to its initial value.

Reproducible: Always

Steps to Reproduce:
1. I open the metadata editor for a single file
2. I copy the artist field and replace the field album artist with the artist. I don't modify any other fields.
3. I click on the "save and close" button. 
4. Absolutely no change
5. I open the metadata editor: no changes were made to the song. The album artist is still "Edison".

Actual Results:  
The track keeps its previous value for "album artist"

Expected Results:  
The track's album artist should have been changed and saved. The ordering by album should have been updated (because the two albums of the tracklist have the same title and different album artists). All this happens correctly if the title is modified at the same time.