installation source (CD) is about 10 times in package list

[LAZA]

i installed Precise alternate beta2 to test an LVM scenario.
after finishing the installation the update icon showed a lot of updates.
opening up the update manager and looking into the sources list, the CD (where i installed from) was listet about 10 times!

BTW:
The standard behavior from Debian is removing the installation source!
Why is this in Ubuntu another way...

Host: Windows 7 SP1
Virtualbox: 4.1.12
Guest: Xubuntu Precise Beta2 (Alternate)

ProblemType: Bug
DistroRelease: Ubuntu 12.04
Package: software-properties-gtk 0.82.7
ProcVersionSignature: Ubuntu 3.2.0-21.34-generic 3.2.13
Uname: Linux 3.2.0-21-generic x86_64
ApportVersion: 2.0-0ubuntu2
Architecture: amd64
Date: Mon Apr 2 21:07:51 2012
EcryptfsInUse: Yes
ExecutablePath: /usr/bin/software-properties-gtk
InstallationMedia: Xubuntu 12.04 LTS "Precise Pangolin" - Beta amd64 (20120327.1)
InterpreterPath: /usr/bin/python2.7
PackageArchitecture: all
ProcEnviron:
 SHELL=/bin/bash
 LANG=de_DE.UTF-8
 PATH=(custom, no user)
SourcePackage: software-properties
UpgradeStatus: No upgrade log present (probably fresh install)

[LAZA (laza74)]

Had this behaviour also with an Quantal installation in an VM

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.