Can't email an .fdf in Acrobat X?

I've been trying to create a .pdf form that the end user can submit via email, and I want to get an .fdf attachment back, not this newfangled autogenerated "file_distributed.pdf" and "file_responses.pdf".
 
I created a SUBMIT button on my form and added code to the Properties/Actions/On Mouseup/Submit a form, where I finally got to select FDF Export Format. I thought I had it made, but when I emailed the form to the user and they hit the submit button, Acrobat Reader X emailed back the "file_distributed.pdf" instead. Ignored the setting in the properties of the Submit button, as far as I can tell. Bummer.
 
Does anyone know how to disable/workaround this new behavior? I already have an .fdf conversion workflow set up, and I'm wondering if Acrobat X is gonna force me to throw out all of that previous work!!!
 
Sheesh. Any thoughts greatly appreciated :-)
 
CR