ubiquity crash with preseed

[Andy Poole]

ubiquity crashes at installing system locales - certain amount of preseeding - could be cause

ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: ubiquity 18.04.14.12 [modified: usr/lib/ubiquity/user-setup/user-setup-apply usr/share/ubiquity/apt-setup]
ProcVersionSignature: Ubuntu 5.0.0-29.31~18.04.1-generic 5.0.21
Uname: Linux 5.0.0-29-generic x86_64
ApportVersion: 2.20.9-0ubuntu7.7
Architecture: amd64
CasperVersion: 1.394
Date: Tue Oct 1 16:19:41 2019
InstallCmdLine: BOOT_IMAGE=/casper/vmlinuz file=/cdrom/preseed/tcc.seed auto=true priority=critical localechooser/languagelist=en localechooser/shortlist=GB localechooser/preferred-locale=en_GB.UTF-8 localechooser/supported-locales=en_GB.UTF-8 debian-installer/language=en keyboard-configuration/layoutcode=gb debian-installer/locale=en_GB.UTF-8 debian-installer/country=GB boot=casper debug-ubiquity automatic-ubiquity initrd=/casper/initrd.gz quiet splash noprompt noshell --
LiveMediaBuild: tcc-xsys-191001 18.04 - Release amd64
ProcEnviron:
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=en_GB.UTF-8
 LC_NUMERIC=C.UTF-8
SourcePackage: ubiquity
UpgradeStatus: No upgrade log present (probably fresh install)