When I type "new message" into HUD, Thunderbird opens two windows instead of one

When I type into the HUD, "new message" and choose Messages > Compose New Message, Thunderbird opens two or three windows to compose an email. I'm pretty sure only one window should appear.
I'm using all the default Unity settings.

Opened Applications: Firefox 11, Empathy 3.3.90.2, and Thunderbird Mail application.

To re-produce, have the applications above open (Not sure if they are necessary for this bug to happen), use the HUD and type in "new message" and then choose the first result which should be Messages > Compose New Message.
You should then see Thunderbird open two or three windows to compose a new email message.

I'm not knowledgable on Ubuntu, but thought I would report this as a Bug, even though it might not be.

ProblemType: Bug
DistroRelease: Ubuntu 12.04
Package: unity 5.6.0-0ubuntu3
ProcVersionSignature: Ubuntu 3.2.0-18.29-generic-pae 3.2.9
Uname: Linux 3.2.0-18-generic-pae i686
.tmp.unity.support.test.0:

ApportVersion: 1.94.1-0ubuntu2
Architecture: i386
CheckboxSubmission: c391cb8855d31638d9d1d099244404d9
CheckboxSystem: b5acb6c9ca4017b1d44043910f45329d
CompizPlugins: [core,composite,opengl,compiztoolbox,decor,vpswitch,snap,mousepoll,resize,place,move,wall,grid,regex,imgpng,session,gnomecompat,animation,fade,unitymtgrabhandles,workarounds,scale,expo,ezoom,unityshell]
CompositorRunning: compiz
Date: Tue Mar 13 19:18:55 2012
DistUpgraded: Log time: 2012-03-10 16:18:30.434928
DistroCodename: precise
DistroVariant: ubuntu
GraphicsCard:
 Advanced Micro Devices [AMD] nee ATI RS780 [Radeon HD 3200] [1002:9610] (prog-if 00 [VGA controller])
   Subsystem: Acer Incorporated [ALI] Device [1025:014e]
InstallationMedia: Ubuntu 12.04 LTS "Precise Pangolin" - Beta i386 (20120301)
MachineType: Acer Aspire M3201
ProcEnviron:
 LANGUAGE=en_GB:en
 TERM=xterm
 LANG=en_GB.UTF-8
 SHELL=/bin/bash
ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-3.2.0-18-generic-pae root=UUID=973f1258-55e4-4b9f-a291-8bb35bb09428 ro quiet splash vt.handoff=7
SourcePackage: unity
UpgradeStatus: Upgraded to precise on 2012-03-12 (0 days ago)
dmi.bios.date: 04/23/2008
dmi.bios.vendor: American Megatrends Inc.
dmi.bios.version: R01-B0
dmi.board.asset.tag: To Be Filled By O.E.M.
dmi.board.name: RS780HVF
dmi.board.vendor: Acer
dmi.chassis.type: 3
dmi.chassis.vendor: Acer
dmi.chassis.version: 1.0
dmi.modalias: dmi:bvnAmericanMegatrendsInc.:bvrR01-B0:bd04/23/2008:svnAcer:pnAspireM3201:pvr:rvnAcer:rnRS780HVF:rvr:cvnAcer:ct3:cvr1.0:
dmi.product.name: Aspire M3201
dmi.sys.vendor: Acer
version.compiz: compiz 1:0.9.7.0+bzr3035-0ubuntu1
version.libdrm2: libdrm2 2.4.30-1ubuntu1
version.libgl1-mesa-dri: libgl1-mesa-dri 8.0.1-0ubuntu2
version.libgl1-mesa-dri-experimental: libgl1-mesa-dri-experimental N/A
version.libgl1-mesa-glx: libgl1-mesa-glx 8.0.1-0ubuntu2
version.xserver-xorg-core: xserver-xorg-core 2:1.11.4-0ubuntu6
version.xserver-xorg-input-evdev: xserver-xorg-input-evdev 1:2.6.99.901+git20120126-0ubuntu2
version.xserver-xorg-video-ati: xserver-xorg-video-ati 1:6.14.99~git20111219.aacbd629-0ubuntu2
version.xserver-xorg-video-intel: xserver-xorg-video-intel 2:2.17.0-1ubuntu4
version.xserver-xorg-video-nouveau: xserver-xorg-video-nouveau 1:0.0.16+git20111201+b5534a1-1build2