Why does my RSS feed duplicate some entries?

When reading my RSS feed with the Thunderbird feed reader, some entries are duplicated. Google Reader does not have the same problem.

Here is the faulty feed: http://plcoder.net/rss.php?rss=Blog

There is a problem, but where?

I added a GUID, but the problem remains. Other feeds do not duplicate like mine, so I will do rework on this module and replace this old good code.

Conclusion: I completely reworked the RSS generator code, and it's OK. I think I was using a very old version of RDF.

Solution

Try adding a <guid> tag to each item, giving it a permalink. i.e.:

<item rdf:about="http://plcoder.net/?doc=2134&amp;amp;titre=mon-pc-se-la-pete">
  <link>http://plcoder.net/?doc=2134&amp;amp;titre=mon-pc-se-la-pete</link>
  <guid>http://plcoder.net/?doc=2134&amp;amp;titre=mon-pc-se-la-pete</guid>
  ...
</item>

Without a GUID, if any of the content in the post changes, your RSS aggregator might think that it is a new post. With the GUID, even if the content of that item changes, your RSS aggregator should just update the post, instead of treating it as a new item.