This bug has been reported to Ubuntu Launchpad as:
https://launchpad.net/bugs/559064

From the original report filed by Alex:

1) Click on Layouts tray icon (flag). Choose 'About'.
2) Layouts icon is removed

ProblemType: Bug
DistroRelease: Ubuntu 10.04
Package: xfce4-panel 4.6.3-1ubuntu2
ProcVersionSignature: Ubuntu 2.6.32-19.28-generic 2.6.32.10+drm33.1
Uname: Linux 2.6.32-19-generic i686
Architecture: i386
Date: Fri Apr 9 12:49:39 2010
ExecutablePath: /usr/bin/xfce4-panel
InstallationMedia: Xubuntu 10.04 "Lucid Lynx" - Beta i386 (20100318)
ProcEnviron:
 LANG=en_US.UTF-8
 SHELL=/bin/bash
SourcePackage: xfce4-panel

XsessionErrors log attached as plain text file:
http://launchpadlibrarian.net/43522647/XsessionErrors.txt


Confirmed by charlie-tca:

I was able to reproduce this issue and obtain a full gdb backtrace. Top of backtrace:

Program received signal SIGSEGV, Segmentation fault.
__strlen_sse2 () at ../sysdeps/i386/i686/multiarch/strlen.S:87
87 ../sysdeps/i386/i686/multiarch/strlen.S: No such file or directory.
 in ../sysdeps/i386/i686/multiarch/strlen.S
(gdb) backtrace full
#0 __strlen_sse2 () at ../sysdeps/i386/i686/multiarch/strlen.S:87
No locals.
#1 0x00e3fd4b in IA__g_strdup (str=0x2 <Address 0x2 out of bounds>) at /build/buildd/glib2.0-2.24.0/glib/gstrfuncs.c:101
        new_str = 0x0
        length = <value optimized out>

Backtrace attachment:
http://launchpadlibrarian.net/43571640/gdb-xkb-plugin.txt

This might be a duplicate of xfce bug 6258, bug 5036, bug 5389 . I do not possess the knowledge to determine if this is duplicate.