[Koha] Zebra indexing issue

[Koller Wolfgang]

Hi all!
 
We are now starting to use Koha in a production environment, and encountered some strange behaviour when it comes to series.
 
We've catalouged some Series which do not have a title, but only a series title. So far no problem. However when searching for them, some times the result shows the correct series title, and sometimes it show "No Title".
 
It seems as if Zebra (which we are using for indexing) sometimes returns the series title as title, and sometimes it wont.
 
Any clues / hints / tips what I can do / check?
 
Regards,
Wolfgang Koller

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