wallpaper doesn't change when /home is on a different partition

[Omega-xis]

this issue is present on my desktop (upgraded from 11.10) and my laptop (fresh 12.04 install)
they both have a seperate /home partition which somehow cannot be accessed while in lightdm login screen which means the greeter doesn't change the wallpaper while browsing all the users...
the wallpapers I've chosen are in /home/niek/pictures which is located on the second partition...

steps to reproduce:
install ubuntu using live-cd or usb-stick.
choose at the partition screen "something else"
creat 3 partitions, 1 for root ("/" --> ext4) one for home ("/home" --> ext4) and a swap partition.
then install ubuntu. at first run change your wallpaper and you'll see it doesn't change in login-screen.

ProblemType: Bug
DistroRelease: Ubuntu 12.04
Package: unity-greeter 0.2.7-0ubuntu1
ProcVersionSignature: Ubuntu 3.2.0-22.35-generic 3.2.14
Uname: Linux 3.2.0-22-generic x86_64
NonfreeKernelModules: nvidia
ApportVersion: 2.0-0ubuntu4
Architecture: amd64
Date: Sat Apr 7 08:52:41 2012
InstallationMedia: Ubuntu 11.04 "Natty Narwhal" - Beta amd64 (20110330)
ProcEnviron:
 LANGUAGE=nl_NL:en
 PATH=(custom, no user)
 LANG=nl_NL.UTF-8
 SHELL=/bin/bash
SourcePackage: unity-greeter
UpgradeStatus: No upgrade log present (probably fresh install)
mtime.conffile..etc.lightdm.unity.greeter.conf: 2012-02-26T10:34:35.572996

[Launchpad Janitor (janitor)]

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