Bug#417590:

[Matt Willsher <matt@monki.org.uk>]

I too have had this problem under Etch stable - thankfully Stephen  
has done the work in finding a work around :)

My disk setup is as follows, all done through partman while running  
the installer in expert mode:

/dev/hda1 \
/dev/hdb1 |- /dev/md0 -> /boot
/dev/hdc1 /

/dev/hda2 \
/dev/hdb2 |- /dev/md1 -> encrypted -> msdos partition -> LVM -> 3 lvs  
(root,var,swap)
/dev/hdc2 /

File systems are all ext3

Regarding the lvm locking, the same also seems to be true for MD  
devices - if you delete the partition tables out the RAID devices  
still show and if then new partitions are added, when it comes to  
creating the new MD devices, it is using the old partition table,  
necessitating a reboot to restart the installer.