When crediting "Ensemble 0" as "0" in the track list of release http://musicbrainz.org/release/3d99f769-12f2-42b3-84bf-2491ccdd7f0c, my edit is taken into account until I reach the last step (Edit note) which shows a void summary. Indeed, entering edit doesn't change anything to the tracklist.
When using Unicode glyph #efbc90 ("０", fullwidth digit zero) instead, as in edit http://musicbrainz.org/edit/26118497, then everything works fine. FYI, "0000", "0x0", etc. are working too. But "0" behaves specially, as if I had entered en empty string.