Banshee should show an empty field for track==0. This issue has been opened in regard to this WONTFIX: http://devzilla.novell.com/taglib-sharp/show_bug.cgi?id=1

Other information:
Just for the record, I'm pasting here the conversation between me and Brian Nickell on #banshee (just after the last messages in the bug at dnc mentioned above):

<knocte>	kerrick_: u there? what I'm trying to say in bug#1 of taglibsharp, is that the track field in ID3v1 is an integer, but in ID3v2 it's a string
<kerrick_>	knocte: TagLib# supports this with Track and TrackCount fields. In the case you mentioned, Tag.Track == 2; Tag.TrackCount == 24. The main problem is that banshee just doesn't show a track count field.
<kerrick_>	It would probably be best, UI-wise to have two spin buttons with a "/" or " of " between them to be, "[ 2] of [ 24]" or something like that.
<kerrick_>	But I have nothing to do with banshee's UI or what is stored in the database.
<knocte>	kerrick_: I see, but ID3v2 allows *any* string in the track field, not only "x/y", so how should banshee or taglib# react when it finds an MP3 with, for example, the string "undefined" or "last track" in that field?
<kerrick_>	I feel the appropriate thing to do in the case of a non-standard string is to label it as zero, especially in the case of an application like banshee which uses the track number to sort files.
<kerrick_>	TagLib# is very flexable internally when it comes to this sort of thing, however. It doesn't set the field until either Track or TrackCount is set, so a file could have a "foobar" track number which would be Track==0, but if the file is edited and saved, the "foobar" field would be unaffected.
<dj-fu>	would it be possible for it to guess which tracknumber the track actually is, and rewrite the tag accordingly?
<dj-fu>	or just pretend the string is actually what it's guessing it to be
<kerrick_>	Moreover, if non-standard track fields are important to Developer X, he could circumvent the Track value completely, and just work with the rawTextIdentificationFrame.
<knocte>	in conclusion, the bug should be opened for banshee..?
<kerrick_>	dj-fu: That would be business for banshee, as TagLib# just deals with basic tag reading/writing. A number of programs do support what you are describing though.
<kerrick_>	knocte: I think in regards to adding a "Track Count" field, but I don't see why banshee should be concerned with non-standard track fields. It's the purpose of a music player and tagging library to cater to the most standard usage.
<knocte>	kerrick_: ok, but now just talking about the "0" string returned from taglib#, should I open a bug for banshee to request for it to present an empty field in that case?
<knocte>	the thing is that most of my music is not sorted by albums so the track field is a non-sense for me
<knocte>	I don't need it
<kerrick_>	Yeah, that makes sense.