Changing target of boatloader during installation process of lubuntu failed.

While installing lubuntu from usb flash drive, installer chose usb stick as default target for bootloader -> failed -> made me choose again, I chose the HDD, it asked again, then it crashed.
A dialog showed up to report this as a bug, in the same time I see another dialog box saying "installation complete... [restart now]"

ProblemType: Bug
DistroRelease: Ubuntu 12.04
Package: ubiquity 2.10.16
ProcVersionSignature: Ubuntu 3.2.0-23.36-generic 3.2.14
Uname: Linux 3.2.0-23-generic x86_64
ApportVersion: 2.0.1-0ubuntu5
Architecture: amd64
CasperVersion: 1.315
Date: Sun May 13 23:31:45 2012
InstallCmdLine: file=/cdrom/preseed/lubuntu.seed boot=casper initrd=/casper/initrd.lz quiet splash --
LiveMediaBuild: Lubuntu 12.04 "Precise Pangolin" - Release amd64 (20120423)
ProcEnviron:
 TERM=unknown
 PATH=(custom, no user)
 LANG=en_US.UTF-8
 SHELL=/bin/bash
SourcePackage: grub-installer
UpgradeStatus: No upgrade log present (probably fresh install)