This bug is sortof a mess in terms of comments because the crash can be triggered with multiple boot loader install failure causes. But the consistently triggerable ones are LDM partition scheme (which grub2 doesn't support at all apparently) and a disk without an MBR gap.
So technically it's a release blocking bug because it's an obviously invalid layout, and anaconda crashes. But at the same time: a.) both are rare cases, with LDM being more common; b.) we're an inch from release so a fix would add more risk than benefit; c.) no prior anaconda could make such a system bootable, although F17's anaconda doesn't crash. The crash itself is a regression.