SSL svn import fails with callback_ssl_server_trust_prompt required

Traceback (most recent call last):
  File "/srv/importd.launchpad.net/production/launchpad-rev-8324/scripts/code-import-worker.py", line 61, in ?
    script.main()
  File "/srv/importd.launchpad.net/production/launchpad-rev-8324/scripts/code-import-worker.py", line 56, in main
    import_worker.run()
  File "/srv/importd.launchpad.net/production/launchpad-rev-8324/lib/lp/codehosting/codeimport/worker.py", line 396, in run
    self._doImport()
  File "/srv/importd.launchpad.net/production/launchpad-rev-8324/lib/lp/codehosting/codeimport/worker.py", line 472, in _doImport
    foreign_tree = self.getForeignTree()
  File "/srv/importd.launchpad.net/production/launchpad-rev-8324/lib/lp/codehosting/codeimport/worker.py", line 426, in getForeignTree
    return self.foreign_tree_store.fetch(self.FOREIGN_WORKING_TREE_PATH)
  File "/srv/importd.launchpad.net/production/launchpad-rev-8324/lib/lp/codehosting/codeimport/worker.py", line 311, in fetch
    return self.fetchFromSource(target_path)
  File "/srv/importd.launchpad.net/production/launchpad-rev-8324/lib/lp/codehosting/codeimport/worker.py", line 316, in fetchFromSource
    branch.checkout()
  File "/srv/importd.launchpad.net/production/launchpad-rev-8324/lib/lp/codehosting/codeimport/foreigntree.py", line 60, in checkout
    svn_client.checkout(
pysvn._pysvn_2_4.ClientError: callback_ssl_server_trust_prompt required
Import failed:
Traceback (most recent call last):
Failure: twisted.internet.error.ProcessTerminated: A process has ended with a probable error condition: process ended with exit code 1.

https://code.edge.launchpad.net/~vcs-imports/blueman/trunk

The server is using a StartCom SSL cert which works without invalid cert warnings on most apps.