I am using feedwordpress and I happen to use WPML in the same site. Every time I updated a feed all post were duplicated, time after time...
It was not until I started debuggung and got the SQL used to find duplicates that it got clear:
SELECT wp_posts.ID, wp_posts.guid, wp_posts.post_modified_gmt
JOIN wp_icl_translations t ON wp_posts.ID = t.element_id
AND t.element_type IN ('post_post','post_page','post_bedrijven') JOIN wp_icl_languages l ON t.language_code=l.code AND l.active=1 WHERE 1=1 AND ((guid = 'http://www.limburger.nl/article/20121105/REGIONIEUWS01/121109319/1008')) ORDER BY wp_posts.post_date DESC
That Feedwordpress is actually integrated with WPML. As far as I can find it is not an option to integrate.
The post type I was using to separate the news posts from other posts was not registered with WPML and because Feedwordpress checks via the wp_icl_translations only duplicates are not found.
I am not interested in the integration Feedwordpress and WPML because news articles will not be translated... so the SQL only produced a lot of overhead.
Can this be an option.