The added comma (in Dutch and maybe also in other languages) is causing issues when importing/exporting .csv, viz. it creates two fields:
1. 'Ander adres' and 2. 'straat'
To avoid this one is required to manually remove the comma's from the header fields after exporting contacts from Outlook to .csv.
One by one, for each field. Or alternatively switch to English before exporting.
The added comma really messes things up when using .csv files.
(not sure whether developers are looking here/whether posting here will reach the developers table at one point in time, or whether I should post in OutlookUserVoice)