I use the email service for receiving emails which stores the attachments into a list of documents. Then I iterate through the list of attachments and extract the filename.
The getDocAttribute() method returns null, but the getDocContentType() method also contains the original filename.
I assume that the receive mail service does not set the attributes correctly.
I think you are right ..... I can assure you that it is set every other way. I have not used it your way yet so I cannot comment on it. I will try it and see.