Maybe MusicBrainz changed this around.
Take the album "Drukqs" by Aphex Twin: http://musicbrainz.org/release/facbe59c-6b...0c-85aaba8d8670
As it says there, it is a 2x15 cd. MusicBrainz also lists the tracks for the seperate discs.
Usually, mp3tag would show this as Drukqs (disc 1) and Drukqs (disc 2), but now it shows only a single 30 track album: Drukqs.
I hope this gets fixed soon 
I will work around it for now, but it will get annoying with time.
Almost a year has passed and I was quite breathtaken to discover that this bug still exists in the latest version...
Am I dreaming this? it's so severe that it makes mass tagging from musicbrainz almost impossible. I mean, thanks to this tiny little annoyance, it gets much more annoying and time consuming to tag. There are no good ways to work around it either. How is it that nobody have bothered about this? It simply can not be true? Am I doing something wrong here?
Or is there an updated web source that I am missing about this?
AFAK are web sources contributions of other mp3tag users who take time and effort to write scripts to extract information from web sites.
So mostly this is an absolutely volountary undertaking.
It is great that these knowledgeable people share their expertise with us.
So if this function you are looking for is of such importance you are welcome to adapt an existing script or write one of your own.
I bet that members of this forum will support you if you are stuck with certain aspects of the syntax.
Well, I do understand that I sound ungrateful, but I don't mean it like that.
And I do get your point of doing my own script, but I'm saying this because mp3tag has had 2 (I think) new releases since after this bug was found. And it still isn't fixed. So it can't be a time issue. If no new releases had been made, then I would not have posted this.
And also, this is core functionality, so I don't think it should be up to the users to have it work.
I don't believe I am the only one using Musicbrainz as my tagging source, and now, tagging from it is almost impossible (or if not picky, highly annoying) because:
If the multi-disc has seperate titles for each disc, Mp3tag can no longer snap this up. One have to go to musicbrainz to see if this is the case, making it very time consuming. No workaround.
It doesnt recognize multi-discs at all anymore. It puts a 2x15 as a 1x30, and numbers them accordingly. Workaround is possible by simply tagging the full 30 tracks and then manually edit. Time consuming/annoying. Especially in conjunction with the first point.
So you see how this is a severe core functionality breakage? And it worked perfectly fine until the Musicbrainz update. I don't mean to sound like an ass here but after one year I expected such a severe bug to be fixed. Especially since it seems so easy to fix (I wouldn't know, however)
MusicBrainz had major changes in their data format.
It will not be possible to have the old way (separate albums for each cd)
All I can do is add proper track and disc numbers for the albums (so it renumbers for each disc)
Thank you for the update on the situation, dano!
I was thinking that there must be a reason for it not to be fixed, and now I know. That is very sad news.
And well, it's not super important, but if you ever get the time, then proper track numbers would make musicbrainz tagging more convenient indeed. At least I would be very thankful for this
Edit: I missed that you wrote "disc number" also. Then this would be very important IMO
As a sidenote, the disc names and numbers can be seen in plain view on musicbrainz.org, so is it not possible to parse them from the page instead of using the api? I don't doubt your words, i'm just curious.