[Zope] sort_on keyword in ZCatalog searches?

[Darran Edmundson]

As per Zen's How-To:
 http://www.zope.org/Members/Zen/howto/AdvZCatalogSearching
I have been trying to sort my ZCatalog searches on a FieldIndex:

<dtml-in "publicationCatalog(Authors='Kivshar',sort_on='Year')">
 <dtml-var Authors>, <dtml-var Journal>,<dtml-var Year></dtml-with><br>
</dtml-in>

On my 2.1.0 Zope, this search returns empty.  On my 2.1.4 Zope,
this search returns a list of the correct length but with duplicate
entries corresponding to the first match.  Year is definately
af FieldIndex.  Any ideas on the source of this problem?

Cheers,
Darran.