ubuntu 12.04 unity-2d-shell crashed with SIGSEGV while dismount a hard disk filesystem

Ubuntu 12.04 Release 12.04 (precise) 64-bit Kernel Linux 3.2.0-23-generic.
While dismount a hard disk filesystem (1TB ext4) unity was blocked for 5 seconds and crashed.
I was not performing other activities.
My system (upgrade of ubuntu 11.10) is updated on 15/04/2012.
Thank you

ProblemType: Crash
DistroRelease: Ubuntu 12.04
Package: unity-2d-shell 5.10.0-0ubuntu1
ProcVersionSignature: Ubuntu 3.2.0-23.36-generic 3.2.14
Uname: Linux 3.2.0-23-generic x86_64
NonfreeKernelModules: nvidia
ApportVersion: 2.0.1-0ubuntu3
Architecture: amd64
CrashCounter: 1
Date: Sun Apr 15 09:28:04 2012
ExecutablePath: /usr/bin/unity-2d-shell
InstallationMedia: Ubuntu 11.10 "Oneiric Ocelot" - Release amd64 (20111012)
ProcCmdline: unity-2d-shell
ProcEnviron:
 PATH=(custom, no user)
 LANG=en_US.UTF-8
 SHELL=/bin/bash
SegvAnalysis:
 Segfault happened at: 0x7f0c7bf1b04a: testb $0x8,0x20(%r15)
 PC (0x7f0c7bf1b04a) ok
 source "$0x8" ok
 destination "0x20(%r15)" (0x1400002025992e0) not located in a known VMA region (needed writable region)!
SegvReason: writing unknown VMA
Signal: 11
SourcePackage: unity-2d
StacktraceTop:
 ?? () from /usr/lib/x86_64-linux-gnu/libQtDeclarative.so.4
 ?? () from /usr/lib/x86_64-linux-gnu/libQtDeclarative.so.4
 ?? () from /usr/lib/x86_64-linux-gnu/libQtDeclarative.so.4
 ?? () from /usr/lib/x86_64-linux-gnu/libQtDeclarative.so.4
 ?? () from /usr/lib/x86_64-linux-gnu/libQtScript.so.4
Title: unity-2d-shell crashed with SIGSEGV
UpgradeStatus: Upgraded to precise on 2012-03-31 (14 days ago)
UserGroups: adm admin cdrom dialout lpadmin plugdev sambashare
XsessionErrors:
 (gnome-settings-daemon:3295): color-plugin-WARNING **: failed to get edid: unable to get EDID for output
 (gnome-settings-daemon:3295): color-plugin-WARNING **: unable to get EDID for xrandr-default: unable to get EDID for output
 (gnome-settings-daemon:3295): color-plugin-WARNING **: failed to reset xrandr-default gamma tables: gamma size is zero
 (gnome-session-properties:4811): GLib-GObject-WARNING **: g_object_set_valist: object class `GsmAppDialog' has no property named `allow-shrink'
 gnome-session[3235]: WARNING: Application 'unity-2d-shell.desktop' killed by signal