Reported at: http://bugs.debian.org/383623
I created a multisession DVD in bonfire, by selecting
the option that says "Leave the disc open to add other
When I later tried to add files to the same DVD, the
burn dialog box showed a notice that said "The DVD-R,
or DVD-RAM is not writable".
dvd+rw-mediainfo reports that the medium is appendable.
I could also successfully append those files using
"growisofs -M" on the command line.