i3 crashed with SIGABRT in __assert_fail_base()

[Benjamin]

i3 was crashed while I used the xlock tool. After the lock was no screen and there was a kernel panic

ProblemType: Crash
DistroRelease: Ubuntu 12.04
Package: i3-wm 4.1.2-2
ProcVersionSignature: Ubuntu 3.2.0-35.55-generic-pae 3.2.34
Uname: Linux 3.2.0-35-generic-pae i686
ApportVersion: 2.0.1-0ubuntu15.1
Architecture: i386
Date: Thu Dec 27 16:48:32 2012
ExecutablePath: /usr/bin/i3
InstallationMedia: Ubuntu 12.04.1 LTS "Precise Pangolin" - Release i386 (20120817.3)
MarkForUpload: True
ProcCmdline: i3 -a --restart /tmp/i3-username.aWgaEj/restart-state.10881
ProcEnviron:
 PATH=(custom, no user)
 LANG=de_DE.UTF-8
 SHELL=/bin/bash
Signal: 6
SourcePackage: i3-wm
StacktraceTop:
 raise () from /lib/i386-linux-gnu/libc.so.6
 abort () from /lib/i386-linux-gnu/libc.so.6
 ?? () from /lib/i386-linux-gnu/libc.so.6
 __assert_fail () from /lib/i386-linux-gnu/libc.so.6
 ?? ()
Title: i3 crashed with SIGABRT in raise()
UpgradeStatus: No upgrade log present (probably fresh install)
UserGroups: adm cdrom dip lpadmin plugdev sambashare sudo vboxusers

[Apport retracing service (apport)]

StacktraceTop:
 __assert_fail_base (fmt=0xb6faf6ca <Address 0xb6faf6ca out of bounds>, assertion=0x808fcc3 "result != ((void *)0)", file=0x808fc2b "src/con.c", line=238, function=0x8090697 <__PRETTY_FUNCTION__.20630> "con_get_output") at assert.c:94
 __GI___assert_fail (assertion=0x808fcc3 "result != ((void *)0)", file=0x808fc2b "src/con.c", line=238, function=0x8090697 <__PRETTY_FUNCTION__.20630> "con_get_output") at assert.c:103
 con_get_output (con=<optimized out>) at src/con.c:238
 con_get_output (con=0x0) at src/con.c:232
 manage_window (window=18874554, cookie=..., needs_to_be_mapped=true) at src/manage.c:286