Description of problem: mdadm 3.2.4 made a major change in the amount of space used for 1.1 and 1.2 metadata in order to reserve space for reshaping. See commit 508a7f16 in the upstream mdadm repository. This has resulted in a large difference between what anaconda thinks the size of the array should be and what it actually is. Depending on the size of the LVM PE and size of the volume you may or may not see errors like: Volume group "vg.first" has insufficient free space (78 extents): 79 required.
anaconda-18.36-1.fc18 has been submitted as an update for Fedora 18. https://admin.fedoraproject.org/updates/anaconda-18.36-1.fc18
Package anaconda-18.36-1.fc18: * should fix your issue, * was pushed to the Fedora 18 testing repository, * should be available at your local mirror within two days. Update it with: # su -c 'yum update --enablerepo=updates-testing anaconda-18.36-1.fc18' as soon as you are able to. Please go to the following url: https://admin.fedoraproject.org/updates/FEDORA-2012-19870/anaconda-18.36-1.fc18 then log in and leave karma (feedback).
anaconda-18.36-1.fc18 has been pushed to the Fedora 18 stable repository. If problems still persist, please make note of it in this bug report.