compiz crashed with SIGSEGV in PrivateWindow::processMap()

[Will]

Binary package hint: unity

Happened when Firefox had finished downloading a file and showed the notify-osd bubble: this has happened several times now.

ProblemType: Crash
DistroRelease: Ubuntu 11.04
Package: unity 3.8.6-0ubuntu1
ProcVersionSignature: Ubuntu 2.6.38-8.42-generic 2.6.38.2
Uname: Linux 2.6.38-8-generic i686
NonfreeKernelModules: wl
Architecture: i386
CrashCounter: 1
Date: Wed Apr 13 21:25:13 2011
ExecutablePath: /usr/bin/compiz
InstallationMedia: Ubuntu 11.04 "Natty Narwhal" - Beta i386 (20110330)
ProcCmdline: compiz
ProcEnviron:
 LANGUAGE=en_GB:en
 LANG=en_GB.UTF-8
 SHELL=/bin/bash
Signal: 11
SourcePackage: unity
StacktraceTop:
 PrivateWindow::processMap() ()
 CompScreen::handleEvent(_XEvent*) ()
 PrivateCompositeScreen::handleEvent(_XEvent*) () from /usr/lib/compiz/libcomposite.so
 CompScreen::handleEvent(_XEvent*) ()
 PrivateGLScreen::handleEvent(_XEvent*) () from /usr/lib/compiz/libopengl.so
Title: compiz crashed with SIGSEGV in PrivateWindow::processMap()
UpgradeStatus: No upgrade log present (probably fresh install)
UserGroups: adm admin cdrom dialout lpadmin plugdev sambashare