Description of problem:
This happened while testing bug 1163410 comment 1. I used a standard ext4 partition, that I tried to shrink in a guided dialog. I selected a value somewhere in the middle of the shrinking slider and confirmed.

Version-Release number of selected component:
anaconda-core-21.48.13-1.fc21.x86_64

The following was filed automatically by anaconda:
anaconda 21.48.13-1 exception report
Traceback (most recent call first):
  File "/tmp/updates/blivet/devices.py", line 1550, in _setTargetSize
    raise ValueError("new size will not yield an aligned partition")
  File "/tmp/updates/blivet/devices.py", line 752, in <lambda>
    lambda s, v: s._setTargetSize(v),
  File "/tmp/updates/blivet/deviceaction.py", line 443, in apply
    self.device.targetSize = self._targetSize
  File "/tmp/updates/blivet/devicetree.py", line 492, in registerAction
    action.apply()
  File "/tmp/updates/blivet/__init__.py", line 1381, in resizeDevice
    self.devicetree.registerAction(action_class(device, new_size))
  File "/usr/lib64/python2.7/site-packages/pyanaconda/ui/gui/spokes/lib/resize.py", line 439, in _scheduleActions
    self.storage.resizeDevice(device, Size(obj.target))
ValueError: new size will not yield an aligned partition

Additional info:
cmdline:        /usr/bin/python  /sbin/anaconda --liveinst --method=livecd:///dev/mapper/live-base --updates=https://dlehman.fedorapeople.org/updates/updates-1163410.0.img
cmdline_file:   BOOT_IMAGE=vmlinuz0 initrd=initrd0.img root=live:CDLABEL=Fedora-Live-Workstation-x86_64-2 rootfstype=auto ro rd.live.image quiet  rhgb rd.luks=0 rd.md=0 rd.dm=0 
executable:     /sbin/anaconda
hashmarkername: anaconda
kernel:         3.17.2-300.fc21.x86_64
other involved packages: anaconda-gui-21.48.13-1.fc21.x86_64
product:        Fedora"
release:        Fedora release 21 (Twenty One)
type:           anaconda
version:        Fedora