Fontconfig - Jan 2009 - font config file: does fontconfig skip bitmap fonts when doing printing?

Hi. I''ve configured my font-config as following:

$ grep -A 6 sans-serif /etc/fonts/conf.d/51-local.conf 
		<family>sans-serif</family>
		<prefer>
			<family>Helvetica</family>
			<family>Droid Sans</family>
			<family>WenQuanYi Bitmap Song</family>
			<family>Droid Sans Fallback</family>
		</prefer>

The intention is

   1.  to use Helvetica for displaying sans-serif text, in case of
      Chinese ideograph, use "WenQuanyi Bitmap Song", both are bitmap
      fonts. "WenQuanyi Bitmap Song" is a font including Chinese
ideographs.
   2. Upon printing, use "Droid Sans" for text, and in case of Chinese
      ideograph, use "Droid Sans Fallback", both are true-type fonts
for
      printing. "Droid Sans Fallback" is a font including Chinese
      ideographs.

In general for display this configuration works perfectly fine, in all
applications (e.g. thunderbird, Firefox).

For printing it messed up. See the example printing:
https://emerson.realss.com/~zhangweiwu/fonts/testcase.ps

The print result:

   1. For English letters, the font is printed using "Droid Sans",
this
      is correctly fall back from Helvetica (I think because Helvetica
      is not available on printer or in system as scalable font);
   2. For Chinese, the font is printed using "WenQuanyi Bitmap Song",
a
      bitmap font, thus mess up printing. It did not fall back to "Droid
      Sans Fallback"(scalable Chinese font) as I wished.

How can I get it work in the way I want?

I am not sure if this is a font-config problem (can I configure it that
way? or a bug in font-config?) or is it a firefox problem (because I
couldn''t test printing from other applications: I can also test with
thunderbird, but it has same core as firefox; I can test abiword or
openoffice but both do not show san-serif in usable font list and both
couldn''t let you choose bitmap font at all). If I asked in the wrong
mailing list, please redirect me to the right one. Thanks.