having similar problem. the value from the field "Save as Attachment Prefix" is never used. Actually the PDF should also be persisted to the "Attachments", if a prefix is specified, but also this doesn't work.

my prefix for a Purchase Order is: ((object.name) + '_' + (object.state) + '_' + (time.ctime()) + ('.pdf'))

but I also tried a simple one like ('PO.pdf')

For pyhon shell syntax training, try this:

pyhon
>>> import time
>>> print "%s" % time.ctime()                               >>Sun Sep  7 22:05:46 2014
>>> print "%s" % time.ctime().split()[4]                >>2014
CTRL-D for quit shell

For attach pdf Sale Order in state 'progress' or 'manual' or 'done' with name 'SO001-2014.pdf', my prefix is:

(object.state in ('progress','manual','done')) and ((object.name or '').replace('/','')+'-'+ time.ctime().split()[4] +'.pdf')

please try with something like this:

(object.state in ('draft','approved')) and ('RfQ_'+(object.name + '_' + time.ctime()).replace('/','')+'.pdf')

Regards

claudio

I had simmilar problem, and finaly foud it out to be a strange bug... On fist print the document name is rendered correct, and stored with correct name, but the file that is downloaded after fisrt rendering is having OLD name value, so the first time you download the attachment it has wrong filename. Also, after downloading, check the name of attachment (clicking on attachments button on top of document page and there the name of document shows up corectly)... 
Instead of rewriting javascript that downloads the document, i just discard the first download, and download it againg from attachment so it gets the desired filename..