I tried to use a lv for /boot. That failed with "lilo does not recognize boot partition" or so very late in the install. I'd assume grub failed as well, therefore it tried lilo as fallback. Although ultimately stupidity on my part the lead to this, I'd have several remarks/suggestions:
1) warn about /boot on a lv during partiotioning
2) warn about grub failing instead of silently try to use lilo
Some more problems I faced later on: I then stepped back in the installer to the partioning and tried to shrink the vg to make space for a normal partion for /boot. I initially had used all available space in the vg. That failed in various steps:
1) vg could not be shrunk.
2) Deleted the lv /home => vg could still not be shrunk
3) Tried to delete all lv => did not work because /swap was already in use
Then I restarted the whole installation. That made the installer to be tun in resuce mode automatically (not sure if that's good or not). I then deleted the lv /sqp and the vg, then created a new vg with 500MB less size. However, I already had 3 primary partitions, so the remaining space was unusabe. After some head-scratching I figured out what I did wrong, deleted the vg again and first made a logical partition and created /boot and the vg in that. Would have been nice to get a better error message here.
This seems to be a problem with the text-mode installer, not the live CD installer. Correct me if I'm wrong.