Hi Jarek,
Thanks for taking the time to look into this (and thanks Trevor for doing the same). At least it seems I'm not the one at fault on this one.
I plan on modifying the properties of each paragraph and leave paragraphStyles as is. Otherwise I would have to cope with duplicate styles, and with 40 languages that won't be a pretty sight. The only paragraphs to be changed are the ones that are located on a given layer and have a specific appliedNumberingList. I wrote a layer/ textframe/ paragraph crawler that does the trick.
Thanks again,
Peter