setup-storage - preserving LUKS partitions possible?

Hello,

I have the following disk config:

disk_config disk1 disklabel:msdos bootable:1 align-at:1 fstabkey:uuid preserve_lazy:6
primary  /boot         1024     ext4    rw
logical  -             30720    -       -
logical  -             40000-   -       -

disk_config lvm
vg vg1 disk1.5
vg1-root  /            23552            ext4    rw,errors=remount-ro
vg1-swap  -             4096            -       -
vg1-tmp   -             1024            -       -
vg1-varlog  /var/log    2048            ext4    rw

disk_config cryptsetup
tmp       -             /dev/vg1/tmp    ext2    -
swap    -               /dev/vg1/swap   swap    -
luks   /media/daten  disk1.6     ext4    acl     createopts="-L Daten"

When reinstalling, setup-storage tells me that it will preserve /dev/sda6, but nevertheless LUKS-formats it again and creates a new filesystem.
Apparently, "preserve" options are not available for cryptsetup blocks, at least according to the manpage. Is there any way to accomplish this?

Thanks,
Andreas