Description of problem:
Installation of F18 with an existing F19 Fedora entry in NVRAM.
The following was filed automatically by anaconda:
anaconda 18.37.11 exception report
Traceback (most recent call first):
  File "/usr/lib64/python2.7/site-packages/pyanaconda/bootloader.py", line 1640, in remove_efi_boot_target
    raise BootLoaderError("failed to remove old efi boot entry")
  File "/usr/lib64/python2.7/site-packages/pyanaconda/bootloader.py", line 1669, in install
    self.remove_efi_boot_target()
  File "/usr/lib64/python2.7/site-packages/pyanaconda/bootloader.py", line 1705, in install
    super(MacEFIGRUB, self).install()
  File "/usr/lib64/python2.7/site-packages/pyanaconda/bootloader.py", line 1689, in write
    self.install()
  File "/usr/lib64/python2.7/site-packages/pyanaconda/bootloader.py", line 2312, in writeBootLoader
    storage.bootloader.write()
  File "/usr/lib64/python2.7/site-packages/pyanaconda/install.py", line 135, in doInstall
    writeBootLoader(storage, payload, instClass, ksdata)
  File "/usr/lib64/python2.7/threading.py", line 504, in run
    self.__target(*self.__args, **self.__kwargs)
  File "/usr/lib64/python2.7/site-packages/pyanaconda/threads.py", line 91, in run
    threading.Thread.run(self, *args, **kwargs)
BootLoaderError: failed to remove old efi boot entry

Additional info:
cmdline:        /usr/bin/python  /sbin/anaconda --liveinst --method=livecd:///dev/mapper/live-osimg-min --lang en_US.UTF-8
cmdline_file:   BOOT_IMAGE=/isolinux/vmlinuz0 root=live:LABEL=Fedora-18-x86_64-Live-Desktop.is ro rd.live.image quiet rhgb
executable:     /sbin/anaconda
hashmarkername: anaconda
kernel:         3.6.10-4.fc18.x86_64
other involved packages: python-libs-2.7.3-13.fc18.x86_64
package:        anaconda-18.37.11-1.fc18.x86_64
product:        Fedora
release:        Fedora release 18 (Spherical Cow)
type:           libreport
version:        18