bzr crashed with AssertionError in lookup_file_id()

lsb_release -rd:
Description: Ubuntu 11.04
Release: 11.04

apt-cache policy bzr:
bzr:
  Installiert: 2.3.1-1ubuntu1
  Kandidat: 2.3.1-1ubuntu1
  Versionstabelle:
 *** 2.3.1-1ubuntu1 0
        500 http://de.archive.ubuntu.com/ubuntu/ natty/main i386 Packages
        100 /var/lib/dpkg/status

The current directory is a git repository. bzr log and in bzr explorer using the menut show log on a file causes the submitted crash. I expected a message, that this function is not implemented yet.

ProblemType: Crash
DistroRelease: Ubuntu 11.04
Package: bzr 2.3.1-1ubuntu1
ProcVersionSignature: Ubuntu 2.6.38-8.42-generic 2.6.38.2
Uname: Linux 2.6.38-8-generic i686
NonfreeKernelModules: nvidia wl
Architecture: i386
BzrDebugFlags: set()
BzrVersion: 2.3.1
CommandLine: ['/usr/bin/bzr', 'log', 'TDObserver.java']
CrashDb: bzr
Date: Fri Jul 8 21:50:24 2011
ExecutablePath: /usr/bin/bzr
FileSystemEncoding: UTF-8
InstallationMedia: Ubuntu 11.04 "Natty Narwhal" - Release i386 (20110427.1)
InterpreterPath: /usr/bin/python2.7
Locale: de_DE.UTF-8
PackageArchitecture: all
Platform: Linux-2.6.38-8-generic-i686-with-Ubuntu-11.04-natty
ProcCmdline: /usr/bin/python /usr/bin/bzr log TDObserver.java
ProcEnviron:
 SHELL=/bin/bash
 PATH=(custom, user)
 LANG=de_DE.UTF-8
 LANGUAGE=de:en
PythonVersion: 2.7.1
SourcePackage: bzr
Title: bzr crashed with AssertionError in lookup_file_id()
UpgradeStatus: No upgrade log present (probably fresh install)
UserEncoding: UTF-8
UserGroups: adm admin cdrom dialout lpadmin plugdev sambashare