feisty fawn herd 2 installer crash: no active autopartitioning choice

It looks like this has been reported a few times, but the installer explicitly told me to post a new bug report. Upon reaching the "Prepare disk space" section, the installer crashed after pausing with the hourglass type cursor for a few minutes.

Traceback (most recent call last):
  File "/usr/lib/ubiquity/bin/ubiquity", line 185, in ?
    main()
  File "/usr/lib/ubiquity/bin/ubiquity", line 180, in main
    install(args[0])
  File "/usr/lib/ubiquity/bin/ubiquity", line 56, in install
    ret = wizard.run()
  File "/usr/lib/ubiquity/ubiquity/frontend/gtkui.py", line 310, in run
    self.process_step()
  File "/usr/lib/ubiquity/ubiquity/frontend/gtkui.py", line 867, in process_step
    self.process_autopartitioning()
  File "/usr/lib/ubiquity/ubiquity/frontend/gtkui.py", line 922, in process_autopartitioning
    choice = self.get_autopartition_choice()[0]
  File "/usr/lib/ubiquity/ubiquity/frontend/gtkui.py", line 1620, in get_autopartition_choice
    raise AssertionError, "no active autopartitioning choice"
AssertionError: no active autopartitioning choice