Duplicate entry warnings on saving categories and containers

Hi,

I've installed the category module in Drupal 5.1, and it's working mostly fine on the frontend. However, whenever I click on "Save categories and containers" I get the following warning six times:

• user warning: Duplicate entry '7-0' for key 1 query: INSERT INTO category_cont_distant (cid, allowed_parent) VALUES (7, '0') in /var/www/drupal/includes/database.mysql.inc on line 172.

(5 more similar warnings)

Any ideas? I've had a look round for similar problems e.g. the long-running thread about $node->parent[0] not existing (and the array_values() patch) but they all seem to pertain to Drupal 4.7, and looking briefly at category.module they seem to have been incorporated into 5.x .

Cheers,
J-P