I've just reinstalled my laptop using the precise alternative amd64 snapshot from 2012-01-27. I wanted to repartition the disk, and then have an lv on a vg on lusk within a partition.
I chose "guided install with encrypted lvm", and I got a luks partition with lvm inside it, but it didn't have any logical volumes. (So, the install could not proceed since there was no root partition.)
I tried again in manual mode and hit the same problem: after the vg was created, I could see it in the partitioner menu, but I couldn't see any way to create an lv within it. When I pressed enter on the pv, or anything connected to it, I was just told "this is in use by $device_name and cannot be edited". (I forget the exact name, it was something like 'crypt_sda5'.)
Please attach /var/log/syslog and /var/log/partman from an installation attempt. You can extract them using "Save debug logs" from the installer main menu, or by running 'anna-install openssh- client- udeb' from a shell and then using scp.