The linked Debian bug appears to describe a similar issue, and includes
this additional PDF displaying the problem. The unknown font tag it
complains of is "G1".
In this case, the size markings from the diagrams, as well as many of
the values in the tables (starting on the second page) display in
** Attachment added: "PDF triggering the bug."
http://launchpadlibrarian.net/27785016/fontspec.pdf
** Attachment added: "Dependencies.txt"
http://launchpadlibrarian.net/27785017/Dependencies.txt
** Bug watch added: Debian Bug tracker #508497
http://bugs.debian.org/cgi-bin/bugreport.cgi?
