UnicodeDecodeError on package gmp and others

$ usd-import --verbose --lp-owner=usd-import-team --directory=gmp --no-push gmp
INFO:root:Ubuntu Server Team importer v1.0-rc2
INFO:root:Cloning git://git.launchpad.net/~usd-import-team/ubuntu/+source/gmp at /importer/work.d/gmp
...
INFO:root:Changelog parent (tag) is import/2%4.2.2+dfsg-3
Importing 2:4.2.2+dfsg-3 to debian/lenny
Importing 2:4.2.2+dfsg-3 to debian/sid
Importing 2:4.2.4+dfsg-2 to debian/sid
Traceback (most recent call last):
  File "/importer/usd-importer/usd-import", line 8, in <module>
    usd.importer.main()
  File "/importer/usd-importer/usd/importer.py", line 278, in main
    [x for x in patch_overrides if x['distribution'] == distname]
  File "/importer/usd-importer/usd/GitRepository.py", line 938, in import_spi
    patch_overrides
  File "/importer/usd-importer/usd/GitRepository.py", line 504, in commit_import
    changelog_parent_commit
  File "/importer/usd-importer/usd/GitRepository.py", line 443, in get_changelog_for_commit
    env=self._env
  File "/usr/lib/python3.5/subprocess.py", line 695, in run
    stdout, stderr = process.communicate(input, timeout=timeout)
  File "/usr/lib/python3.5/subprocess.py", line 1059, in communicate
    stdout = self.stdout.read()
  File "/usr/lib/python3.5/codecs.py", line 321, in decode
    (result, consumed) = self._buffer_decode(data, self.errors, final)
UnicodeDecodeError: 'utf-8' codec can't decode byte 0xe8 in position 2006: invalid continuation byte

I added some debug code and re-ran. the failing command is:
 git diff-tree -p 23e6f885eff092fc7d71807cb4588d78304c0e1b 4c0f7b3b5abe3cdc9456a6
ecc6537248d8f854eb -- debian/changelog

I'm attaching the output of that command.