installation crashed when I went back due to /isodevice still mounted

[Arbiel Perlacremaz]

I always install from an iso file. Ubiquity doesn't know how to unmount this file, mounted on /isodevice. I forgot to do it by hand before asking for the imstallation after I input all necessary data. The crash occurred whem I clicked on the "back" botton".

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: ubiquity 2.21.63.4
ProcVersionSignature: Ubuntu 4.10.0-28.32~16.04.2-generic 4.10.17
Uname: Linux 4.10.0-28-generic x86_64
ApportVersion: 2.20.1-0ubuntu2.10
Architecture: amd64
CasperVersion: 1.376.2
Date: Tue Jan 9 14:07:44 2018
InstallCmdLine: BOOT_IMAGE=/casper/vmlinuz.efi file=/cdrom/preseed/xubuntu.seed boot=casper iso-scan/filename=/amorces/xubuntu-16.04.3-desktop-amd64.iso quiet splash ---
LiveMediaBuild: Xubuntu 16.04.3 LTS "Xenial Xerus" - Release amd64 (20170801)
ProcEnviron:
 LANGUAGE=fr_FR.UTF-8
 PATH=(custom, no user)
 LANG=fr_FR.UTF-8
 SHELL=/bin/bash
SourcePackage: ubiquity
UpgradeStatus: No upgrade log present (probably fresh install)