[ft] Issues with fonts embedded in PDF

[Justus]

Folks,

We're having trouble with some fonts embedded in PDF by Fop, and
thought we might find relevant expertise over here:

Our test file
(http://www.intelsig.be/~piater/nobackup/fop/fop-trunk.pdf) contains
eight embedded TrueType fonts, and is displayed correctly by
Acroread. However, four of these fonts (FreeSerif, latex-xft cmr10,
LinuxLibertine, STIXGeneral converted from OTF using fontforge) just
leave blanks when viewed by xpdf, gv, kpdf, or evince (but copy&paste
ok); the other four are rendered ok (BitstreamVeraSerif, DejaVuSerif,
LiberationSerif, GentiumBasic).

Since all of these four viewers use FreeType, it looks like it might
be a FreeType issue; on the other hand, all of these fonts are
displayed correctly by ftview. Or perhaps it is an embedding (Fop)
issue, but acroread has no trouble.

How to narrow the problem down? Is there anything abnormal about this
PDF file?

Any ideas? Thanks for any help, suggestions or pointers.
Justus