Description of problem:
Attached my 'spare disk' image to my main test VM in order to see if I can reproduce 876789 with software RAID-1. Went into custom partitioning and started removing all existing data from the two drives. One showed as an existing Fedora install - that will be the 15GB disk - and I was able to remove it with no trouble. There was an 'Unknown' entry too, which presumably contained the other disk's partition(s). I say 'presumably' because this crash happened immediately when I tried to expand the Unknown tree.

Version-Release number of selected component:
anaconda-18.29

Additional info:
libreport version: 2.0.17
cmdline:        /usr/bin/python  /sbin/anaconda
kernel:         3.6.6-3.fc18.x86_64

description:
:The following was filed automatically by anaconda:
:anaconda 18.29 exception report
:Traceback (most recent call first):
:  File "/usr/lib64/python2.7/site-packages/pyanaconda/ui/gui/spokes/custom.py", line 1508, in _populate_right_side
:    typeCombo.set_active(type_index_map[device_type])
:  File "/usr/lib64/python2.7/site-packages/pyanaconda/ui/gui/spokes/custom.py", line 1829, in on_selector_clicked
:    self._populate_right_side(selector)
:  File "/usr/lib64/python2.7/site-packages/pyanaconda/ui/gui/spokes/custom.py", line 1693, in _show_first_mountpoint
:    self.on_selector_clicked(page._members[0])
:  File "/usr/lib64/python2.7/site-packages/pyanaconda/ui/gui/spokes/custom.py", line 1847, in on_page_clicked
:    self._show_first_mountpoint(page=page)
:  File "/usr/lib64/python2.7/site-packages/pyanaconda/ui/gui/spokes/lib/accordion.py", line 119, in _onExpanded
:    cb(obj.get_child())
:KeyError: None