Software Center shows several blank debconf window during any installation. I don't know if it is a duplicate of Bug #912708 , because debconf window does not freeze, take a look at the picture.
ProblemType: Bug
DistroRelease: Ubuntu 14.04
Package: software-center 13.10-0ubuntu2
ProcVersionSignature: Ubuntu 3.13.0-1.16-generic 3.13.0-rc7
Uname: Linux 3.13.0-1-generic x86_64
ApportVersion: 2.12.7-0ubuntu6
Architecture: amd64
Date: Fri Jan 10 12:18:00 2014
InstallationDate: Installed on 2014-01-09 (0 days ago)
InstallationMedia: Xubuntu 14.04 LTS "Trusty Tahr" - Alpha amd64 (20140109)
PackageArchitecture: all
ProcEnviron:
LANGUAGE=fr_FR
TERM=xterm
PATH=(custom, no user)
LANG=fr_FR.UTF-8
SHELL=/bin/bash
SourcePackage: software-center
UpgradeStatus: No upgrade log present (probably fresh install)
Status changed to 'Confirmed' because the bug affects multiple users.