Description of problem:
Install problem when using automatic partitioning on a VM with disks
already partitioned in raid.
This problem occured during test of fedora 23 ppc64 Alpha RC2 image.
http://ppc.koji.fedoraproject.org/compose/23_Alpha_RC2/23/Server/ppc64le/iso/Fedora-Server-DVD-ppc64le-23.iso

You must do two installations
Here after is the procedure:
1 First install.

Select 2 disks (20G each) on installation destination
select "I will configure partitioning"
Remove existing partitions if any.
Create new partitions as follow, using "clic here to create them automatically"
/prepboot de 4M standard partition (FS:prepboot)
/boot de 500M en standar partition (FS:)ext4
/swap de 4G en LVM (FS:swap)
/ de 35.5G en LVM (FS:xfs)
Then reduce / partition size to 8G
Create manually a new raid partition
/home de 5G en RAID -> RAID1 (fs:xfs) 
and install the VM.

This VM seems fine and works correctly.

[root@vm53 ~]# df
Filesystem                   1K-blocks    Used Available Use% Mounted on
devtmpfs                       2038336       0   2038336   0% /dev
tmpfs                          2085440       0   2085440   0% /dev/shm
tmpfs                          2085440    4864   2080576   1% /run
tmpfs                          2085440       0   2085440   0% /sys/fs/cgroup
/dev/mapper/fedora_vm53-root   8378368 1601680   6776688  20% /
tmpfs                          2085440      64   2085376   1% /tmp
/dev/sda2                       487652  136597    321359  30% /boot
/dev/md127                     5232640   32960   5199680   1% /home
tmpfs                           417088       0    417088   0% /run/user/0

[root@vm53 ~]# cat /etc/fstab
#
# /etc/fstab
# Created by anaconda on Tue Aug 25 11:52:54 2015
#
# Accessible filesystems, by reference, are maintained under '/dev/disk'
# See man pages fstab(5), findfs(8), mount(8) and/or blkid(8) for more info
#
/dev/mapper/fedora_vm53-root /                       xfs     defaults        0 0
UUID=7ec09897-f401-4c29-88a4-f72a322a0f1f /boot                   ext4    defaults        1 2
UUID=89acb8b7-263e-4aab-8a40-ac394e0c9553 /home                   xfs     defaults        0 0
/dev/mapper/fedora_vm53-swap swap                    swap    defaults        0 0

[root@vm53 ~]# cat /proc/mdstat
Personalities : [raid1] 
md127 : active raid1 sda5[0] sdb2[1]
      10485760 blocks super 1.2 [2/2] [UU]
      [=======>.............]  resync = 37.8% (3966912/10485760) finish=13.6min speed=7977K/sec
      bitmap: 1/1 pages [64KB], 65536KB chunk

unused devices: <none>

[root@vm53 ~]# cat /proc/mdstat 
Personalities : [raid1] 
md127 : active raid1 sda5[0] sdb2[1]
      5242880 blocks super 1.2 [2/2] [UU]
      bitmap: 1/1 pages [64KB], 65536KB chunk

unused devices: <none>

2 Second install

Reboot the VM for a new install.
Select the 2 disks (20G each) used on the previous install
Choose "Automatically configure partitioning" and press "Done"
At this time the anaconda crashes.

Version-Release number of selected component:
anaconda-23.17-1

The following was filed automatically by anaconda:
anaconda 23.17-1 exception report
Traceback (most recent call first):
  File "/usr/lib/python3.4/site-packages/blivet/devices/partition.py", line 485, in removeHook
    "Logical partitions present." % self.name)
  File "/usr/lib/python3.4/site-packages/blivet/devicetree.py", line 227, in _removeDevice
    dev.removeHook(modparent=modparent)
  File "/usr/lib/python3.4/site-packages/blivet/devicetree.py", line 316, in registerAction
    self._removeDevice(action.device)
  File "/usr/lib/python3.4/site-packages/blivet/blivet.py", line 1091, in destroyDevice
    self.devicetree.registerAction(action)
  File "/usr/lib/python3.4/site-packages/blivet/partitioning.py", line 483, in updateExtendedPartitions
    storage.destroyDevice(part)
  File "/usr/lib/python3.4/site-packages/blivet/partitioning.py", line 573, in doPartitioning
    updateExtendedPartitions(storage, disks)
  File "/usr/lib/python3.4/site-packages/blivet/autopart.py", line 501, in doAutoPartition
    doPartitioning(storage)
  File "/usr/lib64/python3.4/site-packages/pyanaconda/kickstart.py", line 346, in execute
    doAutoPartition(storage, ksdata, min_luks_entropy=MIN_CREATE_ENTROPY)
  File "/usr/lib64/python3.4/site-packages/pyanaconda/kickstart.py", line 2179, in doKickstartStorage
    ksdata.autopart.execute(storage, ksdata, instClass)
  File "/usr/lib64/python3.4/site-packages/pyanaconda/ui/gui/spokes/storage.py", line 342, in _doExecute
    doKickstartStorage(self.storage, self.data, self.instclass)
  File "/usr/lib64/python3.4/threading.py", line 868, in run
    self._target(*self._args, **self._kwargs)
  File "/usr/lib64/python3.4/site-packages/pyanaconda/threads.py", line 253, in run
    threading.Thread.run(self, *args, **kwargs)
  File "/usr/lib64/python3.4/site-packages/pyanaconda/threads.py", line 171, in raise_if_error
    raise exc_info[0](exc_info[1]).with_traceback(exc_info[2])
  File "/usr/lib64/python3.4/site-packages/pyanaconda/threads.py", line 93, in get
    self.raise_if_error(name)
  File "/usr/lib64/python3.4/site-packages/pyanaconda/ui/gui/spokes/storage.py", line 371, in completed
    retval = (threadMgr.get(constants.THREAD_EXECUTE_STORAGE) is None and
  File "/usr/lib64/python3.4/site-packages/pyanaconda/ui/gui/hubs/__init__.py", line 217, in _handleCompleteness
    if not spoke.mandatory or spoke.completed:
  File "/usr/lib64/python3.4/site-packages/pyanaconda/ui/gui/hubs/__init__.py", line 211, in _updateCompleteness
    self._handleCompleteness(spoke, update_continue)
  File "/usr/lib64/python3.4/site-packages/pyanaconda/ui/gui/hubs/__init__.py", line 394, in spoke_done
    self._updateCompleteness(sp, update_continue=False)
  File "/usr/lib64/python3.4/site-packages/pyanaconda/ui/gui/spokes/__init__.py", line 59, in on_back_clicked
    self.main_window.current_action.spoke_done(self)
  File "/usr/lib64/python3.4/site-packages/pyanaconda/ui/gui/spokes/storage.py", line 949, in on_back_clicked
    NormalSpoke.on_back_clicked(self, button)
ValueError: Cannot remove extended partition sda4.  Logical partitions present.

Additional info:
addons:         com_redhat_kdump
cmdline:        /usr/bin/python3  /sbin/anaconda
cmdline_file:   BOOT_IMAGE=/ppc/ppc64/vmlinuz ro
dnf.rpm.log:    Aug 26 13:55:34 INFO --- logging initialized ---
executable:     /sbin/anaconda
hashmarkername: anaconda
kernel:         4.2.0-0.rc5.git0.2.fc23.ppc64
product:        Fedora
release:        Cannot get release name.
type:           anaconda
version:        23