partman hangs with lvm raid

i am trying to create a swap partition using lvm's raid, since i cannot create an md device on top of lvm easily. i have done so manually, but when i try and enter the partition manager during installation, the system hangs, and does not respond to any attempt to kill the process. it does get unstuck if i remove the partition, although it complains about the partitions which disappear.

steps to reproduce:

- start installation process
- from the terminal, create an lvm volume group with two physical volumes
- also from the terminal, create a logical volume with --type raid1
- start the partition configuration ui