filter duplicates - cannot get it to work!

Hi,

Please advice on the following issue I am facing.
There is this page I am scraping using the following extractor pattern:

"details link extractor":
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Pattern text: a href="?id=~@ID@~&code=~@CODE@~">

Advanced tab for this extractor patterns has checked the following checkboxes:
- Automatically save the dataset generated by this extractor in a session variable
- If a data set by the same name is found: "Overwrite"
- Filter duplicates
- Cache the data set

The extracted tokens are configured as follow:
~@ID@~ : store in session variable, use to filter duplicates, trim white spaces
~@CODE@~ : store in session variable, trim white spaces
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Within the the page there are the following hrefs I need to get:

As expected the patterns matches all 3 hrefs and stores the tokens in session variables.
My problem is, that acroding to the documentation, in the dataset I should get only 2 of them.

When I press "Test Pattern", is get the following table:
Sequence ID CODE
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0 21 DVD
1 22 DVD
2 22 DVD

ID is something unique and this is why I need to filter by "ID".

Shouldn't the data set contain only first 2 entries (dropping the duplicate ones)?

Please advice.

Best regards.