installer crashed while generating crypto partitions

Installer crashes while creating the second phyiscal encryption volume. The first is always okay.

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: ubiquity 2.21.63
ProcVersionSignature: Ubuntu 4.4.0-21.37-generic 4.4.6
Uname: Linux 4.4.0-21-generic x86_64
ApportVersion: 2.20.1-0ubuntu2
Architecture: amd64
CasperVersion: 1.376
CurrentDesktop: KDE
Date: Sat May 28 09:42:47 2016
InstallCmdLine: BOOT_IMAGE=(loop)/casper/vmlinuz.efi root=UUID=323B-8812 maybe-ubiquity debian-installer/language=de keyboard-configuration/layoutcode=de keyboard-configuration/variantcode=neo iso-scan/filename=/kubuntu-16.04-desktop-amd64.iso boot=casper file=/cdrom/preseed/kubuntu.seed noprompt quiet splash --
LiveMediaBuild: Kubuntu 16.04 LTS "Xenial Xerus" - Release amd64 (20160420.1)
SourcePackage: ubiquity
UpgradeStatus: No upgrade log present (probably fresh install)