mercurial error message when qct installed

While qct is installed, I get the following error when I use various commands in hg (e.g. hg diff):

*** failed to import extension hgext.qct: No module named qct

I purged qct and the error went away.

I then reinstalled qct and the error came back. So this bug is caused while qct is installed, not by an incomplete removal as per another qct bug in the system.

ProblemType: Bug
DistroRelease: Ubuntu 11.10
Package: qct 1.7-1
ProcVersionSignature: Ubuntu 3.0.0-12.20-generic 3.0.4
Uname: Linux 3.0.0-12-generic x86_64
ApportVersion: 1.23-0ubuntu3
Architecture: amd64
Date: Wed Oct 19 15:44:34 2011
InstallationMedia: Ubuntu 11.04 "Natty Narwhal" - Release amd64 (20110427.1)
PackageArchitecture: all
ProcEnviron:
 LANGUAGE=en_GB:en
 PATH=(custom, user)
 LANG=en_GB
 SHELL=/bin/bash
SourcePackage: qct
UpgradeStatus: Upgraded to oneiric on 2011-10-14 (4 days ago)