different 'Blank source' value doesn't update the node

I have a product import from a XML document. To determine the node's published state value I use a blank source with a hardcoded value 1 inside.
When I unpublish my node in the backoffice (Drupal) and run the import again the node is still unpublished. When I change a value for that node in my XML import file and run the import again the published state does get changed.

So if there's nothing changed in the XML file but the blank source value is different the update doesn't get processed.