back to partitioning while luks crypted drive is mounted

[serg_stetsuk]

Ubuntu 15.04 installation over existing luks-crypted lvm partition.
1. Booted Live CD
2. Mounted Encrypted partition
3. Partitioning -> Chose something else -> Configured root swap and boot partitions -> Click next -> click Back ->...Crash

ProblemType: Bug
DistroRelease: Ubuntu 15.04
Package: ubiquity 2.21.25
ProcVersionSignature: Ubuntu 3.19.0-15.15-generic 3.19.3
Uname: Linux 3.19.0-15-generic x86_64
ApportVersion: 2.17.2-0ubuntu1
Architecture: amd64
CasperVersion: 1.360
Date: Tue Oct 13 12:51:04 2015
InstallCmdLine: BOOT_IMAGE=/ubnkern initrd=/ubninit file=/cdrom/preseed/xubuntu.seed boot=casper quiet splash --- persistent
LiveMediaBuild: Xubuntu 15.04 "Vivid Vervet" - Release amd64 (20150422.1)
ProcEnviron:
 LANGUAGE=uk_UA.UTF-8
 PATH=(custom, no user)
 LANG=uk_UA.UTF-8
 SHELL=/bin/bash
SourcePackage: grub-installer
UpgradeStatus: No upgrade log present (probably fresh install)