tpb does not appear to work with Lenovo X220t

I have tried running tpb, but it does not appear to work. There is no output from the example callback being passed as argument.

    % sudo tpb --verbose --thinkpad="xterm" --callback=/usr/share/doc/tpb/callback_example.sh
    There is already a application grabbing some ThinkPad keys.
    Possibly you restarted tpb too fast.

I have stopped the "tpb" service before and made sure, that no other "tpb" process is running in the background.
I have also unloaded the thinkpad_acpi module, which grabs most of the keys otherwise (e.g. "Lock screen").

I also tried "--xevents=off", but apart from the warning not being displayed, it did not appear to make it work either.

The same applies to using 0.6.4-6 from Debian.

ProblemType: Bug
DistroRelease: Ubuntu 12.04
Package: tpb 0.6.4-2.3ubuntu3
ProcVersionSignature: Ubuntu 3.2.0-8.15-generic-pae 3.2.0
Uname: Linux 3.2.0-8-generic-pae i686
ApportVersion: 1.90-0ubuntu1
Architecture: i386
Date: Thu Jan 12 23:56:37 2012
EcryptfsInUse: Yes
InstallationMedia: Ubuntu 11.04 "Natty Narwhal" - Release i386 (20110427.1)
SourcePackage: tpb
UpgradeStatus: Upgraded to precise on 2011-12-16 (27 days ago)