OK, some more info on this:
If I set the post status to 'public' in the importer, the result is a bit strange too - the posts don't show up anywhere in the dashboard, but the number of posts under 'All' in the post counter continues to rise by the number of documents found by the importer. Basically, the importer seems to be capable of creating posts in the database to which there is no interface in wordpress - no way to view them and no way to delete them.
I'd really appreciate some help with this. I have to get this working for a client who has over 300 documents to set up, and obviously doing that manually for each one would take a lot of time. I am simply using the bulk importer as is, only changing the paths apart from that one experiment with the post status.