[DNSB]

That would suggest that you were not actually using the OBOK plugin since it's code is independent from the DeDRM plugins code. Did you click on an OBOK icon in the toolbar and then use the list of books generated from either the desktop app or a connected ereader to select which books to import? Or were you adding ePubs using the Add books tool or dragging/dropping them on calibre?

Also note that a Kobo epub synced from Kobo which is what OBOK works on does not have an human readable filename, the filename looks much like a GUID such 0a7a1c48-c2d5-4b50-a177-a634110132e7.