Traceback (most recent call last):
  File "/usr/lib/ubiquity/ubiquity/frontend/gtk_ui.py", line 1337, in watch_debconf_fd_helper
    return callback(source, debconf_condition)
  File "/usr/lib/ubiquity/ubiquity/filteredcommand.py", line 253, in process_input
    self.exit_ui_loops()
  File "/usr/lib/ubiquity/plugins/ubi-partman.py", line 2780, in exit_ui_loops
    self.preseed('grub-installer/bootdev', self.ui.get_grub_choice())
  File "/usr/lib/ubiquity/ubiquity/filteredcommand.py", line 338, in preseed
    self.db.set(name, value)
  File "/usr/lib/python2.7/dist-packages/debconf.py", line 65, in <lambda>
    lambda *args, **kw: self.command(command, *args, **kw))
  File "/usr/lib/python2.7/dist-packages/debconf.py", line 69, in command
    self.write.write("%s %s\n" % (command, ' '.join(map(str, params))))
ValueError: I/O operation on closed file