That file prints duplex no matter what printer I send it to. After examining it I believe it has to do with the structure rather than file type. The post script files are structured differently and I'm thinking there is something in them that prevents duplex printing on the command line. I haven't figured out how print one of the problem postscript files in windows 100% determine if it is just a 'nix bug or a postscript file bug.
Rather than fight the troublesome attachement system here, I'll post a link to the files in my dropbox.
The header information from a sample postscript file
https://dl.dropboxusercontent.com/u/405468/postscriptheader.txt
a sample postscript file that we have used to test
https://dl.dropboxusercontent.com/u/405468/TMP20130426150418LEEEL_edited.ps