Not sure I was so clear (writing from my mobile phone...)
So, there are two problems here:
1. The internal download directory seems to be downloading a single NZB file in subdirectories instead of a flat directory structure (all the nzb files into the same directory), this may be causing problems with newsbin detecting multipar/autopar completion correctly and repairing files. I can do it manually if put all the files it downloaded into the same directory and then run multipar manually.
2. the unrar should be targeting the nzb (or file name) under the unrar dir. Instead, some files are now unraring to the root unrar directory.
I put my unrar file on top, the NZB watch folder and other filters don't have specific unrar or download dir settings (they are empty)