package gnome-session 3.11.4-0ubuntu1~trusty2 [origin: LP-PPA-gnome3-team-gnome3-staging] failed to install/upgrade: a tentar sobre-escrever '/usr/share/upstart/sessions/gnome-session.conf', que também está no pacote gnome-session-bin 3.9.90-0ubuntu12

After install gnome 3.12, this message appears.

ProblemType: Package
DistroRelease: Ubuntu 14.04
Package: gnome-session 3.11.4-0ubuntu1~trusty2 [origin: LP-PPA-gnome3-team-gnome3-staging]
ProcVersionSignature: Ubuntu 3.13.0-24.46-generic 3.13.9
Uname: Linux 3.13.0-24-generic x86_64
ApportVersion: 2.14.1-0ubuntu3
Architecture: amd64
Date: Wed Apr 23 20:13:46 2014
DuplicateSignature: package:gnome-session:3.11.4-0ubuntu1~trusty2 [origin: LP-PPA-gnome3-team-gnome3-staging]:a tentar sobre-escrever '/usr/share/upstart/sessions/gnome-session.conf', que também está no pacote gnome-session-bin 3.9.90-0ubuntu12
ErrorMessage: a tentar sobre-escrever '/usr/share/upstart/sessions/gnome-session.conf', que também está no pacote gnome-session-bin 3.9.90-0ubuntu12
InstallationDate: Installed on 2014-04-18 (5 days ago)
InstallationMedia: Ubuntu-GNOME 14.04 LTS "Trusty Tahr" - Release amd64 (20140416.2)
PackageArchitecture: all
SourcePackage: gnome-session
Title: package gnome-session 3.11.4-0ubuntu1~trusty2 [origin: LP-PPA-gnome3-team-gnome3-staging] failed to install/upgrade: a tentar sobre-escrever '/usr/share/upstart/sessions/gnome-session.conf', que também está no pacote gnome-session-bin 3.9.90-0ubuntu12
UpgradeStatus: No upgrade log present (probably fresh install)