Description of problem:
Trying to confugre custom partition options in Anaconda installer

Version-Release number of selected component:
anaconda-core-25.19-1.fc25.x86_64

The following was filed automatically by anaconda:
anaconda 25.19-1 exception report
Traceback (most recent call first):
  File "/usr/lib/python3.5/site-packages/blivet/devicetree.py", line 406, in get_disk_actions
    if any(action.device.depends_on(d) for d in disks):
  File "/usr/lib/python3.5/site-packages/blivet/threads.py", line 45, in run_with_lock
    return m(*args, **kwargs)
  File "/usr/lib/python3.5/site-packages/blivet/devicetree.py", line 425, in cancel_disk_actions
    actions = self.get_disk_actions(disks)
  File "/usr/lib/python3.5/site-packages/blivet/threads.py", line 45, in run_with_lock
    return m(*args, **kwargs)
  File "/usr/lib/python3.5/site-packages/blivet/devicetree.py", line 819, in hide
    self.cancel_disk_actions(device)
  File "/usr/lib/python3.5/site-packages/blivet/threads.py", line 45, in run_with_lock
    return m(*args, **kwargs)
  File "/usr/lib64/python3.5/site-packages/pyanaconda/ui/gui/spokes/storage.py", line 834, in _hide_disks
    self.storage.devicetree.hide(disk)
  File "/usr/lib64/python3.5/site-packages/pyanaconda/ui/gui/spokes/storage.py", line 961, in on_back_clicked
    self._hide_disks()
TypeError: 'DiskDevice' object is not iterable

Additional info:
cmdline:        /usr/bin/python3  /sbin/anaconda --liveinst --method=livecd:///dev/mapper/live-base
cmdline_file:   BOOT_IMAGE=vmlinuz initrd=initrd.img root=live:CDLABEL=Fedora-KDE-Live-Rawhide-20160629 rd.live.image nomodeset quiet
executable:     /sbin/anaconda
hashmarkername: anaconda
kernel:         4.7.0-0.rc5.git1.1.fc25.x86_64
other involved packages: anaconda-gui-25.19-1.fc25.x86_64, python3-blivet-2.1.1-1.fc25.noarch
product:        Fedora
release:        Fedora release 25 (Rawhide)
reproducible:   Not sure how to reproduce the problem
type:           anaconda
version:        rawhide