Install media unusable after the oem setup installation

The usb key becomes unusable once its used for a oem setup installation. Re-creating the startu disk is the only way to recover from this.

Steps to reproduce:

1) Create a usb installation media with http://cdimage.ubuntu.com/precise/daily-live/20120817.3/precise-desktop-i386.iso
2) Follow the steps http://testcases.qa.ubuntu.com/Install/DesktopOem to carry out the oem installation.
3) Follow the steps in http://testcases.qa.ubuntu.com/Install/DesktopFree to perform another installation

** At this point it could be noticed that the installation screen will go back to OEM installation setup as shown in the attached image

ProblemType: Bug
DistroRelease: Ubuntu 12.04
Package: ubiquity (not installed)
ProcVersionSignature: Ubuntu 3.2.0-29.46-generic-pae 3.2.24
Uname: Linux 3.2.0-29-generic-pae i686
ApportVersion: 2.0.1-0ubuntu12
Architecture: i386
Date: Mon Aug 20 15:05:56 2012
InstallCmdLine: noprompt cdrom-detect/try-usb=true persistent file=/cdrom/preseed/ubuntu.seed boot=casper only-ubiquity initrd=/casper/initrd.lz quiet splash -- apt-setup/restricted=false apt-setup/multiverse=false
InstallationMedia: Ubuntu 12.04.1 LTS "Precise Pangolin" - Release i386 (20120817.3)
ProcEnviron:
 LANGUAGE=en_GB:en
 TERM=xterm
 PATH=(custom, no user)
 LANG=en_GB.UTF-8
 SHELL=/bin/bash
SourcePackage: ubiquity
UpgradeStatus: No upgrade log present (probably fresh install)