Import branch stuck: UnicodeDecodeError during get_log

My import branch has been stuck for ages now: https://code.launchpad.net/~vcs-imports/libpqxx/trunk/

The tracebacks all look the same, ending in:

«
  File "/srv/importd.launchpad.net/production/launchpad-rev-16430/lib/cscvs/bzr.py", line 160, in commitWithAutomaticLog
    message = revision.get_log().decode('utf-8', 'replace')
  File "/srv/importd.launchpad.net/production/launchpad-rev-16430/lib/svn_oo/Revision.py", line 114, in get_log
    return self.log['message'].encode('utf8')
UnicodeDecodeError: 'ascii' codec can't decode byte 0xc3 in position 87: ordinal not in range(128)
»

When I try to restart the import from the UI, by clicking "Try again", it oopses consistently — OOPS-e35fb1779da06920ba5044dc9b8cd5af OOPS-8a4b37f23993b8e89380797d40b886cf OOPS-77a94863320097640b73c45c45d21478.