Description of problem:
I tried to update settings of disk partitioning during installation

Version-Release number of selected component:
anaconda-20.18-1.fc20.x86_64

The following was filed automatically by anaconda:
anaconda 20.18-1 exception report
Traceback (most recent call first):
  File "/usr/lib/python2.7/site-packages/blivet/__init__.py", line 1948, in copy
    root.swaps = [new.devicetree.getDeviceByID(d.id) for d in root.swaps]
  File "/usr/lib/python2.7/site-packages/blivet/devicefactory.py", line 767, in _save_devicetree
    _blivet_copy = self.storage.copy()
  File "/usr/lib/python2.7/site-packages/blivet/devicefactory.py", line 704, in configure
    self._save_devicetree()
  File "/usr/lib/python2.7/site-packages/blivet/__init__.py", line 1924, in factoryDevice
    factory.configure()
  File "/usr/lib64/python2.7/site-packages/pyanaconda/ui/gui/spokes/custom.py", line 1069, in _replace_device
    new_device = self.__storage.factoryDevice(*args, **kwargs)
  File "/usr/lib64/python2.7/site-packages/pyanaconda/ui/gui/spokes/custom.py", line 1362, in _save_right_side
    selector=selector)
  File "/usr/lib64/python2.7/site-packages/pyanaconda/ui/gui/spokes/custom.py", line 2790, in on_apply_clicked
    self._save_right_side(self._current_selector)
AttributeError: 'NoneType' object has no attribute 'id'

Additional info:
cmdline:        /usr/bin/python  /sbin/anaconda --liveinst --method=livecd:///dev/mapper/live-osimg-min --lang en_US.UTF-8
cmdline_file:   initrd=initrd0.img root=live:CDLABEL=Fedora-Live-Desktop-x86_64-20-Al rootfstype=auto ro rd.live.image quiet  rhgb rd.luks=0 rd.md=0 rd.dm=0  BOOT_IMAGE=vmlinuz0 
executable:     /sbin/anaconda
hashmarkername: anaconda
kernel:         3.11.0-300.fc20.x86_64
other involved packages: python-blivet-0.20-1.fc20.noarch
product:        Fedora
release:        Fedora release 20 (Heisenbug)
type:           anaconda
version:        20