In Ubuntu Karmic Ingo Ruhnke reported:

Using Ubuntu 9.10 and Rhythmbox 0.12.5 it happens every now and then that two completly different podcast episodes from different feeds get merged into one. The title and the feed column then show info from one episode, but the underlying MP3 and time column as well as the description point to a different episode of a different podcast feed. One such entry would be (taken from /home/ingo/.local/share/rhythmbox/rhythmdb.xml):

  <entry type="podcast-post">
    <title>Item #372 - How To Sing To A Preschooler</title> <-- (1)
    <genre>Podcast</genre>
    <artist>Dr Chris Smith, The Naked Scientists</artist> <-- (2)
    <album>One Minute How-To</album> <-- (1)
    <duration>3935</duration>
    <file-size>23658468</file-size>
    <location>file:///share/podcasts/One%20Minute%20How-To/Naked_Scientists_Show_09.11.01.mp3</location> <-- (2)
    <mountpoint>http://nakeddiscovery.com/libsyn/Naked_Scientists_Show_09.11.01.mp3</mountpoint> <-- (2)
    <first-seen>1266515408</first-seen>
    <rating>2.5</rating>
    <bitrate>48</bitrate>
    <date>0</date>
    <mimetype>application/x-id3</mimetype>
    <status>100</status>
    <description>The most distant object ever discovered as well as the events of National Pathology week feature in this week's show as we take on your science questions! We investigate whysocks go missing in the wash, whether light from the sun is a continuous beam and whether numerous vaccines can be given together in one dose. We also find out how higher heels make for a better runner and reveal the world's fastest camera. Plus, we find out why we get a better signal when holding an aerial and show you how to make a helicopter using card and pencils!</description> <- (2)
    <subtitle>http://feeds.feedburner.com/OneMinuteHowTo</subtitle> <- (1)
    <summary></summary>
    <lang></lang>
    <copyright></copyright>
    <image></image>
    <post-time>1266469260</post-time>
    <mb-trackid></mb-trackid>
    <mb-artistid></mb-artistid>
    <mb-albumid></mb-albumid>
    <mb-albumartistid></mb-albumartistid>
    <mb-artistsortname></mb-artistsortname>
    <album-sortname></album-sortname>
  </entry>

The feeds are:

1) http://feeds.feedburner.com/OneMinuteHowTo
2) http://www.thenakedscientists.com/naked_scientists_podcast.xml

There don't seem to be any obvious naming conflicts between the feeds or the MP3 that could explain the behavior. I don't have a way to reproduce it, but it has happened to me multiple times with different Podcasts.

Launchpad ref: https://bugs.edge.launchpad.net/ubuntu/+source/rhythmbox/+bug/525535

Thanks