The ubuntu software-center doesn't open, it's loading without any result o screen until it crashes.
Although the test description above does not describe this, I found that I could reproduce this crash as follows:
TEST CASE:
1. open stock software-center
2. click on the "All Software" button very quickly while the main page is still loading
3. verify that there is a traceback (note that this does not happen always, just most of the time)
4. use the fixed version from -proposed
5. verify that (2) no longer produces a traceback
ProblemType: Crash
DistroRelease: Ubuntu 12.04
Package: software-center 5.1.6
ProcVersionSignature: Ubuntu 3.2.0-10.17-generic 3.2.1
Uname: Linux 3.2.0-10-generic i686
ApportVersion: 1.91-0ubuntu1
Architecture: i386
Date: Mon Jan 23 00:22:16 2012
ExecutablePath: /usr/share/software-center/software-center
InstallationMedia: Ubuntu 12.04 LTS "Precise Pangolin" - Alpha i386 (20111129.1)
InterpreterPath: /usr/bin/python2.7
PackageArchitecture: all
ProcCmdline: /usr/bin/python /usr/bin/software-center
ProcEnviron:
PATH=(custom, no user)
LANG=el_GR.UTF-8
SHELL=/bin/bash
PythonArgs: ['/usr/bin/software-center']
SourcePackage: software-center
Title: software-center crashed with AttributeError in __contains__(): 'NoneType' object has no attribute '__contains__'
UpgradeStatus: Upgraded to precise on 2012-01-22 (0 days ago)
UserGroups: adm cdrom dip lpadmin plugdev sambashare sudo
Status changed to 'Confirmed' because the bug affects multiple users.