Difference in behaviour for Super-num vs Super-Shift-Num

When pressing Super-Shift-2 to launch a new terminal, I have to press Super first and then press Shift, otherwise the action is ignored.

To reproduce:
 * Press Super then 2
 * See the terminal focus
 * Press Super then very quickly press 2
 * See the terminal focus
 * Hold Super, pause ~100 ms, Hold Shift, press 2
 * See a new terminal launch
 * Press Super and Shift at the same time, then press 2
 * No terminal starts

I normally end up with a '@' on my screen instead...

ProblemType: Bug
DistroRelease: Ubuntu 12.04
Package: unity 5.6.0-0ubuntu3
ProcVersionSignature: Ubuntu 3.2.0-18.29-generic 3.2.9
Uname: Linux 3.2.0-18-generic x86_64
NonfreeKernelModules: fglrx
ApportVersion: 1.94.1-0ubuntu2
Architecture: amd64
CompizPlugins: [core,composite,opengl,decor,vpswitch,snap,compiztoolbox,resize,regex,animation,move,place,gnomecompat,mousepoll,grid,imgpng,unitymtgrabhandles,workarounds,session,wall,expo,fade,scale,unityshell]
Date: Fri Mar 16 16:11:04 2012
InstallationMedia: Ubuntu 12.04 LTS "Precise Pangolin" - Alpha amd64 (20120219)
ProcEnviron:
 SHELL=/bin/bash
 TERM=xterm
 PATH=(custom, no user)
 LANG=en_NZ.UTF-8
 LANGUAGE=en_NZ:en
SourcePackage: unity
UpgradeStatus: No upgrade log present (probably fresh install)