Having repoze.what installed breaks launchpad scripts

I had installed python-repoze.what to check it out, but it broke a 'make schema' for my launchpad environment. apt-get remove python-repoze.what meant I could continue working, but is sub-optimal as I'd like to have it installed.

Evident using: bin/py to start an interpreter.

>>> import site
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/tim/src/launchpad/branch-subscription-subscribed-by/parts/scripts/site.py", line 601, in <module>
    main()
  File "/home/tim/src/launchpad/branch-subscription-subscribed-by/parts/scripts/site.py", line 586, in main
    paths_in_sys = addsitepackages(paths_in_sys)
  File "/home/tim/src/launchpad/branch-subscription-subscribed-by/parts/scripts/site.py", line 359, in addsitepackages
    addsitedir(path, known_paths)
  File "/home/tim/src/launchpad/branch-subscription-subscribed-by/parts/scripts/site.py", line 164, in addsitedir
    addpackage(sitedir, name, known_paths)
  File "/home/tim/src/launchpad/branch-subscription-subscribed-by/parts/scripts/site.py", line 133, in addpackage
    exec line
  File "<string>", line 1, in <module>
KeyError: 'repoze.what'
>>>