Closing lid doesnt suspend (Vostro 3750)

When closing the lid, my system doesn't suspend although configured to do so (Unity settings)
- Pressing suspend on the bar works.
- /etc/acpi/lid.sh gets called but only turns off the screen

-> Dont know though wether this is a Unity, X or ACPI-problem..

adding a /etc/acpi/local/lid.sh.post does works though:

#!/bin/sh
grep -q closed /proc/acpi/button/lid/*/state
if [ $? = 0 ]
then
    /usr/sbin/pm-suspend
fi

ProblemType: Bug
DistroRelease: Ubuntu 11.10
Package: acpi-support 0.138
ProcVersionSignature: Ubuntu 3.0.0-15.26-generic-pae 3.0.13
Uname: Linux 3.0.0-15-generic-pae i686
NonfreeKernelModules: wl
ApportVersion: 1.23-0ubuntu4
Architecture: i386
Date: Sat Feb 11 19:47:09 2012
InstallationMedia: Ubuntu 11.10 "Oneiric Ocelot" - Release i386 (20111012)
ProcEnviron:
 PATH=(custom, no user)
 LANG=de_DE.UTF-8
 SHELL=/bin/bash
SourcePackage: acpi-support
UpgradeStatus: No upgrade log present (probably fresh install)
modified.conffile..etc.acpi.events.lidbtn: [modified]
mtime.conffile..etc.acpi.events.lidbtn: 2012-02-11T19:42:37.536211