[DVIPDFMx] Filter specification in pdf:stream command

[Dino Petrucci]

It seems that "pdf:stream" command, in "dvipdfmx" (dvipdfmx-20090708), doesn't 
accept any filter. For example, I compile the following program using TeX:

  XMP metadata.
  \special{pdf:stream @metadata (All XMP metadata) << /Type /Metadata /Subtype 
/XML /Filter null >>}
  \special{pdf:put @catalog << /Metadata @metadata >>}
  \bye

Then by the command "dvipdfmx <program_name>.dvi" I get the PDF. In PDF I find

  5 0 obj
  <</Type/Metadata/Subtype/XML/Filter/FlateDecode/Length 24>>
  stream
  x�s��Q��
  P�M-ILI,I ,o�
  endstream

but it's not correct. I tried any kind of filter name (and without filter 
specification): I always get "/Filter/FlateDecode". Why?
Thanks.

Dino Petrucci