bzr crashed with RuntimeError in _sub_group(): maximum recursion depth exceeded

I was updating trunk in my sample project after I imported a language package into the trunk without unzipping it.

ProblemType: Crash
DistroRelease: Ubuntu 11.04
Package: bzr 2.3.4-0ubuntu1
ProcVersionSignature: Ubuntu 2.6.38-11.48-generic 2.6.38.8
Uname: Linux 2.6.38-11-generic x86_64
NonfreeKernelModules: nvidia
Architecture: amd64
BzrDebugFlags: set()
BzrVersion: 2.3.4
CheckboxSubmission: 71ff7045e50f7487de5137ac74798ccd
CheckboxSystem: edda5d4f616ca792bf437989cb597002
CommandLine: ['/usr/bin/bzr', 'explorer']
CrashDb: bzr
Date: Fri Aug 26 15:10:47 2011
ExecutablePath: /usr/bin/bzr
FileSystemEncoding: UTF-8
InstallationMedia: Ubuntu 11.04 "Natty Narwhal" - Release amd64 (20110427.1)
InterpreterPath: /usr/bin/python2.7
Locale: nl_NL.UTF-8
PackageArchitecture: all
Platform: Linux-2.6.38-11-generic-x86_64-with-Ubuntu-11.04-natty
ProcCmdline: /usr/bin/python /usr/bin/bzr explorer
ProcEnviron:
 LANGUAGE=nl_NL:en
 LANG=nl_NL.UTF-8
 SHELL=/bin/bash
PythonVersion: 2.7.1
SourcePackage: bzr
Title: bzr crashed with RuntimeError in _sub_group(): maximum recursion depth exceeded
UpgradeStatus: No upgrade log present (probably fresh install)
UserEncoding: UTF-8
UserGroups: adm admin cdrom dialout lpadmin plugdev sambashare