Shift+AltGr is not mapped to the Compose key

[pabouk]

They Compose Key documentation says:
https://help.ubuntu.com/community/ComposeKey

...
4. From [Layouts] tab click Options... (or Layout Options... pre 10.04)
5. Expand the listing of Compose key position options [+].
6. if no box is ticked then the Shift+AltGr (Right Alt Key) is the Compose key (also called the Multi_Key in Xwindow documentation).

I have Ubuntu 14.04 64 bit but Shift+AltGr does not work as Compose key (I have tried both left and right Shift). I have tested this both with the English (US) and Czech (qwerty) keyboards.

"xkbprint :0" command shows for the keycode 108 (the AltGr key):
- in English (US) layout: Alt_R / with Shift: Meta_R
- in Czech (qwerty) layout: ISO_Level3_Shift (both without and with Shift)
Those keysyms show in xev.

In System Settings > Keyboard > Shortcuts > Typing if I define Compose Key to Right Ctrl or Caps Lock then it works with the selected key as expected. The selected key has keysym Multi_key in xkbprint.

ProblemType: Bug
DistroRelease: Ubuntu 14.04
Package: xorg 1:7.7+1ubuntu8
ProcVersionSignature: Ubuntu 3.13.0-32.57-generic 3.13.11.4
Uname: Linux 3.13.0-32-generic x86_64
.tmp.unity.support.test.0:

ApportVersion: 2.14.1-0ubuntu3.2
Architecture: amd64
CompizPlugins: No value set for `/apps/compiz-1/general/screen0/options/active_plugins'
CompositorRunning: compiz
CompositorUnredirectDriverBlacklist: '(nouveau|Intel).*Mesa 8.0'
CompositorUnredirectFSW: true
CurrentDesktop: Unity
Date: Sun Jul 27 15:05:40 2014
DistUpgraded: Fresh install
DistroCodename: trusty
DistroVariant: ubuntu
ExtraDebuggingInterest: Yes
GraphicsCard:
 Intel Corporation 4th Gen Core Processor Integrated Graphics Controller [8086:0416] (rev 06) (prog-if 00 [VGA controller])
   Subsystem: Lenovo Device [17aa:2211]
 NVIDIA Corporation GK208M [GeForce GT 730M] [10de:1290] (rev a1) (prog-if 00 [VGA controller])
   Subsystem: Lenovo Device [17aa:2211]
InstallationDate: Installed on 2014-07-18 (9 days ago)
InstallationMedia: Ubuntu 14.04 LTS "Trusty Tahr" - Release amd64 (20140417)
MachineType: LENOVO 20BE005YMC
ProcKernelCmdLine: BOOT_IMAGE=/vmlinuz-3.13.0-32-generic.efi.signed root=/dev/mapper/ubuntu--vg-root ro quiet splash vt.handoff=7
SourcePackage: xorg
UpgradeStatus: No upgrade log present (probably fresh install)
dmi.bios.date: 05/15/2014
dmi.bios.vendor: LENOVO
dmi.bios.version: GMET65WW (2.13 )
dmi.board.asset.tag: Not Available
dmi.board.name: 20BE005YMC
dmi.board.vendor: LENOVO
dmi.board.version: 0B98401 Pro
dmi.chassis.asset.tag: No Asset Information
dmi.chassis.type: 10
dmi.chassis.vendor: LENOVO
dmi.chassis.version: Not Available
dmi.modalias: dmi:bvnLENOVO:bvrGMET65WW(2.13):bd05/15/2014:svnLENOVO:pn20BE005YMC:pvrThinkPadT540p:rvnLENOVO:rn20BE005YMC:rvr0B98401Pro:cvnLENOVO:ct10:cvrNotAvailable:
dmi.product.name: 20BE005YMC
dmi.product.version: ThinkPad T540p
dmi.sys.vendor: LENOVO
version.compiz: compiz 1:0.9.11.1+14.04.20140701-0ubuntu1
version.ia32-libs: ia32-libs N/A
version.libdrm2: libdrm2 2.4.52-1
version.libgl1-mesa-dri: libgl1-mesa-dri 10.1.3-0ubuntu0.1
version.libgl1-mesa-dri-experimental: libgl1-mesa-dri-experimental N/A
version.libgl1-mesa-glx: libgl1-mesa-glx 10.1.3-0ubuntu0.1
version.xserver-xorg-core: xserver-xorg-core 2:1.15.1-0ubuntu2
version.xserver-xorg-input-evdev: xserver-xorg-input-evdev 1:2.8.2-1ubuntu2
version.xserver-xorg-video-ati: xserver-xorg-video-ati 1:7.3.0-1ubuntu3.1
version.xserver-xorg-video-intel: xserver-xorg-video-intel 2:2.99.910-0ubuntu1
version.xserver-xorg-video-nouveau: xserver-xorg-video-nouveau 1:1.0.10-1ubuntu2
xserver.bootTime: Sun Jul 27 10:18:56 2014
xserver.configfile: default
xserver.errors:
 Failed to load module "nvidia" (module does not exist, 0)
 Failed to load module "nvidia" (module does not exist, 0)
 NOUVEAU(G0): Error creating GPU channel: -19
 NOUVEAU(G0): Error initialising acceleration. Falling back to NoAccel
xserver.logfile: /var/log/Xorg.0.log
xserver.outputs:
 product id 38562
 vendor MEI
xserver.version: 2:1.15.1-0ubuntu2