See
http://forums.musicbrainz.org/viewtopic.php?pid=22120

The search server is currently returning

<medium-list>
  <track-count>8</track-count>
  <medium>
    <format>CD</format>
    <disc-list count="30"/>
    <track-list count="8"/>
  </medium>
</medium-list>

but previous versions, and the main ws/2 include a count="1" attribute on medium-list there. This appears to be a regression from the 2012-05-15 schema change release.