Installer crashed @ partition stage

It seemed to have some kind of issue. As an aside, I'd appreciate a clearer description of what the "Install along Windows X" option does.

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
Date: Sat May 14 19:17:27 2016
InstallCmdLine: initrd=/casper/initrd.lz file=/cdrom/preseed/ubuntu.seed boot=casper quiet splash --- persistent BOOT_IMAGE=/casper/vmlinuz.efi
LiveMediaBuild: Ubuntu 16.04 LTS "Xenial Xerus" - Release amd64 (20160420.1)
ProcEnviron:
 PATH=(custom, no user)
 LANG=en_US.UTF-8
 SHELL=/bin/bash
SourcePackage: ubiquity
UpgradeStatus: No upgrade log present (probably fresh install)