[TYPO3-Solr] Duplicate results after adding a facet

[Jigal van Hemert]

Hi,

To be able to search in a particular branch of a site I added a dynamic 
field:

[PIDinRootline = 3,37,38,39,54,55]
plugin.tx_solr.index.queue.pages.fields.area_stringS = TEXT
plugin.tx_solr.index.queue.pages.fields.area_stringS {
   data = leveltitle:1
}
[global]

and defined a facet

section {
   field = area_stringS
   label = Sectie
   includeInAvailableFacets = 1
}

After re-indexing the facet shows up and works, but... suddenly some of 
the results (only in content type pages) have duplicate items. Exactly 
the same url to exactly the same page, same modify date and even the 
same word highlighted.

How can we prevent those duplicate results?

-- 
Kind regards / met vriendelijke groet,

Jigal van Hemert.