[merge-upstream] unclear message when upstream version could not be found

I was trying to use 'bzr mu' to update Ubuntu's mutter today. It's a standard gnome package with a standard watch file. Perhaps the one thing tripping bzr-builddeb is that the last version was 3.0.2.1 and the new version I want is 3.1.4.

https://code.launchpad.net/~ubuntu-branches/ubuntu/oneiric/mutter/oneiric

$ bzr mu
Using distribution oneiric
Using version string 3.0.2.1.
Using uscan to look for the upstream tarball.
mutter: Version (3.0.2.1) available on remote site:
  http://ftp.gnome.org/pub/GNOME/sources/mutter/3.0/mutter-3.0.2.1.tar.bz2
  (local version is 3.0.2.1)
^Cbzr: interrupted
==
I manually stopped this because merging 3.0.2.1 on to 3.0.2.1 isn't what I want to do.
==

$ bzr mu --version 3.1.4
Using distribution oneiric
Using version string 3.1.4.
Using uscan to look for the upstream tarball.
uscan warning: In /tmp/tmpniSBVp no matching hrefs for version 3.1.4 in watch line
  http://ftp.gnome.org/pub/GNOME/sources/mutter/([\d\.]+)\d/ mutter-(.*)\.tar\.bz2
uscan could not find the needed tarball.
bzr: ERROR: mutter 3.1.4 was not found in <bzrlib.plugins.builddeb.upstream.UScanSource object at 0x3138dd0>.

ProblemType: Bug
DistroRelease: Ubuntu 11.10
Package: bzr-builddeb 2.7.7
ProcVersionSignature: Ubuntu 3.0.0-9.12-generic 3.0.3
Uname: Linux 3.0.0-9-generic x86_64
Architecture: amd64
Date: Tue Aug 23 23:53:05 2011
InstallationMedia: Ubuntu 11.10 "Oneiric Ocelot" - Alpha amd64 (20110822)
PackageArchitecture: all
ProcEnviron:
 PATH=(custom, no user)
 LANG=en_US.UTF-8
 SHELL=/bin/bash
SourcePackage: bzr-builddeb
UpgradeStatus: No upgrade log present (probably fresh install)