gnome-panel fails when VNC is active

[L_d_v_c@]

Hello
When I run Xvncviewer to take control on my family's computer on Gnomem then gnome-panel fails

lsb_release -rd
Description: Ubuntu 12.04.1 LTS
Release: 12.04

apt-cache policy gnome-panel
gnome-panel:
  Installé : 1:3.4.1-0ubuntu1.1
  Candidat : 1:3.4.1-0ubuntu1.1
 Table de version :
 *** 1:3.4.1-0ubuntu1.1 0
        500 http://fr.archive.ubuntu.com/ubuntu/ precise-updates/universe amd64 Packages
        100 /var/lib/dpkg/status
     1:3.4.1-0ubuntu1 0
        500 http://fr.archive.ubuntu.com/ubuntu/ precise/universe amd64 Packages

ProblemType: Bug
DistroRelease: Ubuntu 12.04
Package: gnome-panel 1:3.4.1-0ubuntu1.1
ProcVersionSignature: Ubuntu 3.2.0-31.50-generic 3.2.28
Uname: Linux 3.2.0-31-generic x86_64
NonfreeKernelModules: nvidia
ApportVersion: 2.0.1-0ubuntu13
Architecture: amd64
Date: Sat Oct 6 22:35:07 2012
InstallationMedia: Ubuntu 12.04 LTS "Precise Pangolin" - Release amd64 (20120425)
ProcEnviron:
 TERM=xterm
 PATH=(custom, no user)
 LANG=fr_FR.UTF-8
 SHELL=/bin/bash
SourcePackage: gnome-panel
UpgradeStatus: No upgrade log present (probably fresh install)