Usually I use easytag for editing my mp3 files tags. Sometimes I do little modifications with amarok. easytag has a field for saving the total number of tracks on the album. For the CD number I use a format like "1/2" (first CD of a two CD set). This works fine for example with iTunes. So far I thought amarok just ignored that information. Now I've just discovered when I use amarok to edit a completely unrelated tag (like genre) it purges all that information. The total tracks field is deleted and the CD field becomes just "1".
See related KDE forums post at http://forum.kde.org/viewtopic.php?f=116&t=91283
As already stated in the forum, I can't reproduce that with Amarok 2.4.-git of tooday. Amarok only displays the first number in the CD tag, nothing else. No tags are rewritten, checking the tags with easytag shows that it still reads 1/2. So this is most likely a parsing error.
Just tested this again with Amarok 2.4.0 / KDE 4.5.5 on Archlinux and this bug seems to have vanished. Changed status to RESOLVED / FIXED, hope that this is ok. Thanks to the Amarok team!