metacity uninstallable on Quantal: metacity : Depends: libmetacity-private0a (= 1:2.34.3-3ubuntu1) but it is not going to be installed

[Jean-Baptiste Lallement]

On Quantal up-to-date

$ sudo apt-get install -o Debug::pkgProblemResolver=1 metacity
Reading package lists... Done
Building dependency tree
Reading state information... Done
Starting
Starting 2
Investigating (0) compiz-gnome [ amd64 ] < 1:0.9.8+bzr3319-0ubuntu1 > ( x11 )
Broken compiz-gnome:amd64 Depends on libmetacity-private0 [ amd64 ] < 1:2.34.1-1ubuntu11 > ( libs ) (>= 1:2.26.0)
  Considering libmetacity-private0:amd64 1 as a solution to compiz-gnome:amd64 5
  Added libmetacity-private0:amd64 to the remove list
  Fixing compiz-gnome:amd64 via keep of libmetacity-private0:amd64
Investigating (0) libmetacity-private0a [ amd64 ] < none -> 1:2.34.3-3ubuntu1 > ( libs )
Broken libmetacity-private0a:amd64 Breaks on libmetacity-private0 [ amd64 ] < 1:2.34.1-1ubuntu11 > ( libs )
  Considering libmetacity-private0:amd64 1 as a solution to libmetacity-private0a:amd64 0
  Holding Back libmetacity-private0a:amd64 rather than change libmetacity-private0:amd64
Investigating (1) metacity [ amd64 ] < 1:2.34.1-1ubuntu11 -> 1:2.34.3-3ubuntu1 > ( x11 )
Broken metacity:amd64 Depends on libmetacity-private0a [ amd64 ] < none -> 1:2.34.3-3ubuntu1 > ( libs ) (= 1:2.34.3-3ubuntu1)
  Considering libmetacity-private0a:amd64 0 as a solution to metacity:amd64 10000
  Re-Instated libmetacity-private0a:amd64
Investigating (1) libmetacity-private0a [ amd64 ] < none -> 1:2.34.3-3ubuntu1 > ( libs )
Broken libmetacity-private0a:amd64 Breaks on libmetacity-private0 [ amd64 ] < 1:2.34.1-1ubuntu11 > ( libs )
  Considering libmetacity-private0:amd64 1 as a solution to libmetacity-private0a:amd64 0
  Holding Back libmetacity-private0a:amd64 rather than change libmetacity-private0:amd64
Investigating (2) metacity [ amd64 ] < 1:2.34.1-1ubuntu11 -> 1:2.34.3-3ubuntu1 > ( x11 )
Broken metacity:amd64 Depends on libmetacity-private0a [ amd64 ] < none -> 1:2.34.3-3ubuntu1 > ( libs ) (= 1:2.34.3-3ubuntu1)
  Considering libmetacity-private0a:amd64 0 as a solution to metacity:amd64 10000
Done
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:

The following packages have unmet dependencies:
 metacity : Depends: libmetacity-private0a (= 1:2.34.3-3ubuntu1) but it is not going to be installed
E: Unable to correct problems, you have held broken packages.

ProblemType: Bug
DistroRelease: Ubuntu 12.10
Package: metacity 1:2.34.1-1ubuntu11
ProcVersionSignature: Ubuntu 3.5.0-11.11-generic 3.5.2
Uname: Linux 3.5.0-11-generic x86_64
ApportVersion: 2.5.1-0ubuntu2
Architecture: amd64
Date: Fri Aug 24 10:05:17 2012
ProcEnviron:
 TERM=xterm
 PATH=(custom, user)
 LANG=en_US.UTF-8
 SHELL=/bin/bash
SourcePackage: metacity
UpgradeStatus: Upgraded to quantal on 2012-01-31 (205 days ago)