Great, both the search and also the filters works fine after the update to 6.4.27. Just a small quirk. Searching with for example "country:Sverige" works fine in Search and Filters, but "country:Sweden" doesn't despite using English as the languish in Groupoffice.
The country data for the old contacts in the data base is lost. I think it happened after updating from 6.3 to 6.4, but I'm not hundred percent sure. The country informations for organizations are fine.