@Marco:

Below is debug output from running compiz --replace. I ran this command with the external monitor already plugged in. After restarting compiz, the window decorations draw correctly on both screens.

1) Plug in external monitor
2) Open a terminal
3) Type compiz --replace. UI becomes unresponsive (the mouse still moved around, but I couldn't interact with windows)
4) I switched to another VT to see what was happening. top reported apport was running
5) I switched back to VT7; compiz restarted


steve@aether:~$ compiz --replace
compiz (core) - Info: Loading plugin: core
compiz (core) - Info: Starting plugin: core
compiz (core) - Info: Loading plugin: ccp
compiz (core) - Info: Starting plugin: ccp
compizconfig - Info: Backend     : gsettings
compizconfig - Info: Integration : true
compizconfig - Info: Profile     : unity
compiz (core) - Info: Loading plugin: composite
compiz (core) - Info: Starting plugin: composite
compiz (core) - Info: Loading plugin: opengl
compiz (core) - Info: Unity is fully supported by your hardware.
compiz (core) - Info: Unity is fully supported by your hardware.
compiz (core) - Info: Starting plugin: opengl
compiz (core) - Info: Loading plugin: copytex
compiz (core) - Info: Starting plugin: copytex
compiz (core) - Info: Loading plugin: imgpng
compiz (core) - Info: Starting plugin: imgpng
compiz (core) - Info: Loading plugin: move
compiz (core) - Info: Starting plugin: move
compiz (core) - Info: Loading plugin: place
compiz (core) - Info: Starting plugin: place
compiz (core) - Info: Loading plugin: commands
compiz (core) - Info: Starting plugin: commands
compiz (core) - Info: Loading plugin: vpswitch
compiz (core) - Info: Starting plugin: vpswitch
compiz (core) - Info: Loading plugin: mousepoll
compiz (core) - Info: Starting plugin: mousepoll
compiz (core) - Info: Loading plugin: resize
compiz (core) - Info: Starting plugin: resize
compiz (core) - Info: Loading plugin: compiztoolbox
compiz (core) - Info: Starting plugin: compiztoolbox
compiz (core) - Info: Loading plugin: regex
compiz (core) - Info: Starting plugin: regex
compiz (core) - Info: Loading plugin: grid
compiz (core) - Info: Starting plugin: grid
compiz (core) - Info: Loading plugin: snap
compiz (core) - Info: Starting plugin: snap
compiz (core) - Info: Loading plugin: wall
compiz (core) - Info: Starting plugin: wall
compiz (core) - Info: Loading plugin: unitymtgrabhandles
compiz (core) - Info: Starting plugin: unitymtgrabhandles
compiz (core) - Info: Loading plugin: session
compiz (core) - Info: Starting plugin: session
compiz (core) - Info: Loading plugin: animation
compiz (core) - Info: Starting plugin: animation
compiz (core) - Info: Loading plugin: expo
compiz (core) - Info: Starting plugin: expo
compiz (core) - Info: Loading plugin: workarounds
compiz (core) - Info: Starting plugin: workarounds
compiz (core) - Info: Loading plugin: fade
compiz (core) - Info: Starting plugin: fade
compiz (core) - Info: Loading plugin: ezoom
compiz (core) - Info: Starting plugin: ezoom
compiz (core) - Info: Loading plugin: scale
compiz (core) - Info: Starting plugin: scale
compiz (core) - Info: Loading plugin: unityshell
compiz (core) - Info: Starting plugin: unityshell
WARN  2014-04-14 11:54:47 unity.glib.dbus.server GLibDBusServer.cpp:579 Can't register object 'org.gnome.Shell' yet as we don't have a connection, waiting for it...
ERROR 2014-04-14 11:54:47 unity.debug.interface DebugDBusInterface.cpp:196 Unable to load entry point in libxpathselect: libxpathselect.so.1.4: cannot open shared object file: No such file or directory
WARN  2014-04-14 11:54:47 xim.controller XIMController.cpp:103 IBus natively supported.
WARN  2014-04-14 11:54:47 unity.glib.dbus.server GLibDBusServer.cpp:579 Can't register object 'com.canonical.Unity.Launcher' yet as we don't have a connection, waiting for it...
WARN  2014-04-14 11:54:47 unity.glib.dbus.server GLibDBusServer.cpp:579 Can't register object 'com.canonical.Unity.Dash' yet as we don't have a connection, waiting for it...
WARN  2014-04-14 11:54:48 unity.glib.dbus.server GLibDBusServer.cpp:579 Can't register object 'org.gnome.SessionManager.EndSessionDialog' yet as we don't have a connection, waiting for it...
WARN  2014-04-14 11:54:48 unity.glib.dbus.server GLibDBusServer.cpp:579 Can't register object 'com.canonical.Unity.Session' yet as we don't have a connection, waiting for it...
WARN  2014-04-14 11:54:48 unity.glib.dbus.server GLibDBusServer.cpp:579 Can't register object 'org.gnome.ScreenSaver' yet as we don't have a connection, waiting for it...
ERROR 2014-04-14 11:54:48 unity.glib.dbus.server GLibDBusServer.cpp:524 DBus name lost 'org.gnome.Shell'
ERROR 2014-04-14 11:54:48 unity.glib.dbus.server GLibDBusServer.cpp:524 DBus name lost 'com.canonical.Unity'