DistUpgradeViewNonInteractive produces error on conffile-prompt from dpkg

When running $do-release-upgrade -f DistUpgradeViewNonInteractive -p on an x64 Ubuntu 14.04 host a conf file prompt for /etc/issue results in:
"ERROR error ''str' does not support the buffer interface' when trying to write to the conffile"

System info:
lsb_release -rd
Description: Ubuntu 14.04.5 LTS
Release: 14.04

apt-cache policy ubuntu-release-upgrader-core
ubuntu-release-upgrader-core:
  Installed: 1:0.220.8
  Candidate: 1:16.04.17
  Version table:
     1:16.04.17 0
        500 http://us.archive.ubuntu.com/ubuntu/ xenial-updates/main amd64 Packages
     1:16.04.12 0
        500 http://us.archive.ubuntu.com/ubuntu/ xenial/main amd64 Packages
 *** 1:0.220.8 0
        100 /var/lib/dpkg/status

Partial output of main.log:

2016-11-07 12:53:36,005 DEBUG disabling apt cron job (0o755)
2016-11-07 13:01:06,388 DEBUG plugins for condition 'StartUpgrade' are '[]'
2016-11-07 13:01:06,388 DEBUG plugins for condition 'xenialStartUpgrade' are '[]'
2016-11-07 13:01:06,388 DEBUG plugins for condition 'from_trustyStartUpgrade' are '[]'
2016-11-07 13:01:06,389 DEBUG quirks: running StartUpgrade
2016-11-07 13:01:06,389 DEBUG skipping 'README' (no '.')
2016-11-07 13:01:06,390 DEBUG killing update-notifier
2016-11-07 13:01:06,403 DEBUG killing kblueplugd kbluetooth4
2016-11-07 13:01:06,409 DEBUG killing gnome-screensaver
2016-11-07 13:01:06,417 DEBUG setup poke timer for the scrensaver
2016-11-07 13:01:06,421 DEBUG failed to determine user upgrading
2016-11-07 13:01:06,421 ERROR failed to inhibit gnome-session idle
2016-11-07 13:01:06,421 DEBUG apt btrfs snapshots supported: False
2016-11-07 13:01:06,421 INFO cache.commit()
2016-11-07 13:01:06,421 DEBUG failed to SystemUnLock() (E:Not locked)
2016-11-07 13:01:06,669 DEBUG doing a pty.fork()
2016-11-07 13:01:06,671 DEBUG pid is: 1729
2016-11-07 13:01:26,498 WARNING got a conffile-prompt from dpkg for file: '/etc/issue'
2016-11-07 13:01:31,499 ERROR error ''str' does not support the buffer interface' when trying to write to the conffile
2016-11-07 13:41:26,327 WARNING no activity 2400 seconds (Configuring base-files (amd64)) - sending ctrl-c
2016-11-07 13:41:26,371 ERROR not handled exception:
Traceback (most recent call last):
  File "/tmp/ubuntu-release-upgrader-b1xls5f6/xenial", line 8, in <module>
    sys.exit(main())
  File "/tmp/ubuntu-release-upgrader-b1xls5f6/DistUpgrade/DistUpgradeMain.py", line 242, in main
    if app.run():
  File "/tmp/ubuntu-release-upgrader-b1xls5f6/DistUpgrade/DistUpgradeController.py", line 1876, in run
    return self.fullUpgrade()
  File "/tmp/ubuntu-release-upgrader-b1xls5f6/DistUpgrade/DistUpgradeController.py", line 1841, in fullUpgrade
    if not self.doDistUpgrade():
  File "/tmp/ubuntu-release-upgrader-b1xls5f6/DistUpgrade/DistUpgradeController.py", line 1182, in doDistUpgrade
    res = self.cache.commit(fprogress,iprogress)
  File "/tmp/ubuntu-release-upgrader-b1xls5f6/DistUpgrade/DistUpgradeCache.py", line 267, in commit
    apt.Cache.commit(self, fprogress, iprogress)
  File "/usr/lib/python3/dist-packages/apt/cache.py", line 501, in commit
    res = self.install_archives(pm, install_progress)
  File "/usr/lib/python3/dist-packages/apt/cache.py", line 465, in install_archives
    res = install_progress.run(pm)
  File "/tmp/ubuntu-release-upgrader-b1xls5f6/DistUpgrade/DistUpgradeView.py", line 234, in run
    res = os.WEXITSTATUS(self.wait_child())
  File "/tmp/ubuntu-release-upgrader-b1xls5f6/DistUpgrade/DistUpgradeView.py", line 200, in wait_child
    self.update_interface()
  File "/tmp/ubuntu-release-upgrader-b1xls5f6/DistUpgrade/DistUpgradeViewNonInteractive.py", line 221, in update_interface
    os.write(self.master_fd,chr(3))
TypeError: 'str' does not support the buffer interface

2016-11-07 13:41:26,371 DEBUG confirmRestart() called
2016-11-07 13:41:26,372 DEBUG enabling apt cron job