When using two displays with different vertical resolution, icons get lost on the shorter display.

[Problem]
When using two displays with different vertical resolution, icons get lost on the shorter display.

[Test Case]
1. Set up two monitors side by side
2. Set left monitor to a smaller vertical resolution than the right monitor
3. for i in $(seq 1 50) ; do touch file-${i} ; done
4. Right click on desktop to bring up context menu, then 'Organize Desktop by Name'
5. Should be: All icons from file-1 to file-50 (or as many fit on the screen) should be visible
     Is: Icons for files at the top and/or bottom of the arranged columns are not visible on any display
6. xrandr --output LVDS1 --off
7. Verify icons are arranged properly on the external monitor
8. Set up monitors one over the other
9. Verify icons are displayed in long columns spanning both displays with all icons shown

[Original Report]
while this long standing problem has been mitigated with some previous work and patches (eg: #389519) at least keeping the mouse away from the dead area, the desktop behaviour is far from being precise still.

when using a couple of monitors with different vertical resolution, icons can easily get lost on the shortest monitor, to reproduce the bug just put on the shortest monitor enough icons to exceed a single column, click on the desktop with the right mouse button and then "organize desktop by name".

another issue is with compiz corner hotspots bindings, they are never triggered if there's a dead area above or below them, it depends on where your shortest display is aligned in respect of the tallest (top or bottom margin), to reproduce try for example to bind the "Show Desktop" action on a corner of the shortest display.

lsb_release -rd
Description: Ubuntu 11.10
Release: 11.10
---
.tmp.unity.support.test.0:

ApportVersion: 1.23-0ubuntu4
Architecture: amd64
CompizPlugins: [core,bailer,detection,composite,opengl,decor,vpswitch,snap,gnomecompat,imgpng,mousepoll,compiztoolbox,wall,grid,move,obs,regex,place,unitymtgrabhandles,resize,animation,workarounds,session,fade,expo,scale,ezoom,unityshell]
CompositorRunning: compiz
DistUpgraded: Fresh install
DistroCodename: oneiric
DistroRelease: Ubuntu 11.10
DistroVariant: ubuntu
DkmsStatus:
 fglrx, 8.902, 3.0.0-12-generic, x86_64: installed
 vboxhost, 4.1.6, 3.0.0-12-generic, x86_64: installed
 virtualbox, 4.1.2, 3.0.0-12-generic, x86_64: installed (WARNING! Diff between built and installed module!) (WARNING! Diff between built and installed module!) (WARNING! Diff between built and installed module!) (WARNING! Diff between built and installed module!)
ExtraDebuggingInterest: Yes, if not too technical
GraphicsCard:
 ATI Technologies Inc Manhattan [Mobility Radeon HD 5400 Series] [1002:68e0] (prog-if 00 [VGA controller])
   Subsystem: Hewlett-Packard Company Device [103c:1601]
InstallationMedia: Ubuntu 11.10 "Oneiric Ocelot" - Release amd64 (20111012)
JockeyStatus:
 xorg:fglrx_updates - ATI/AMD proprietary FGLRX graphics driver (post-release updates) (Proprietary, Disabled, Not in use)
 xorg:fglrx - ATI/AMD proprietary FGLRX graphics driver (Proprietary, Enabled, In use)
MachineType: Hewlett-Packard HP Pavilion dv3 Notebook PC
NonfreeKernelModules: fglrx
Package: xorg 1:7.6+7ubuntu7
PackageArchitecture: amd64
ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-3.0.0-12-generic root=UUID=93cfa569-59f6-4894-8653-97e9e1060ad8 ro quiet splash pcie_aspm=force vt.handoff=7
ProcVersionSignature: Ubuntu 3.0.0-12.20-generic 3.0.4
Tags: oneiric running-unity ubuntu compiz-0.9
Uname: Linux 3.0.0-12-generic x86_64
UpgradeStatus: No upgrade log present (probably fresh install)
UserGroups: adm admin cdrom dialout lpadmin plugdev sambashare vboxusers www-data
dmi.bios.date: 07/08/2010
dmi.bios.vendor: Hewlett-Packard
dmi.bios.version: F.11
dmi.board.asset.tag: Base Board Asset Tag
dmi.board.name: 1601
dmi.board.vendor: Hewlett-Packard
dmi.board.version: 58.1F
dmi.chassis.asset.tag: CNU03411W4
dmi.chassis.type: 10
dmi.chassis.vendor: Hewlett-Packard
dmi.chassis.version: Chassis Version
dmi.modalias: dmi:bvnHewlett-Packard:bvrF.11:bd07/08/2010:svnHewlett-Packard:pnHPPaviliondv3NotebookPC:pvr05A0110000203010000020100:rvnHewlett-Packard:rn1601:rvr58.1F:cvnHewlett-Packard:ct10:cvrChassisVersion:
dmi.product.name: HP Pavilion dv3 Notebook PC
dmi.product.version: 05A0110000203010000020100
dmi.sys.vendor: Hewlett-Packard
version.compiz: compiz 1:0.9.6+bzr20110929-0ubuntu5
version.fglrx-installer: fglrx-installer N/A
version.ia32-libs: ia32-libs 20090808ubuntu26
version.libdrm2: libdrm2 2.4.26-1ubuntu1
version.libgl1-mesa-dri: libgl1-mesa-dri 7.11-0ubuntu3
version.libgl1-mesa-dri-experimental: libgl1-mesa-dri-experimental N/A
version.libgl1-mesa-glx: libgl1-mesa-glx 7.11-0ubuntu3
version.xserver-xorg: xserver-xorg 1:7.6+7ubuntu7
version.xserver-xorg-input-evdev: xserver-xorg-input-evdev 1:2.6.0-1ubuntu13
version.xserver-xorg-video-ati: xserver-xorg-video-ati 1:6.14.99~git20110811.g93fc084-0ubuntu1
version.xserver-xorg-video-intel: xserver-xorg-video-intel 2:2.15.901-1ubuntu2
version.xserver-xorg-video-nouveau: xserver-xorg-video-nouveau 1:0.0.16+git20110411+8378443-1