Have you inserted a reference into a text box or something similar? I am not sure how OpenOffice handles those, just that Word handles them in a funny order, or ignores them entirely?
no, there are no citations in any boxes or anything similar. just simple text.
but now something really strange happened:
When I opened the document again [23] was [22]. And when I inserted a new reference, [22] became the correct [23] again and the new reference was correct as well.