hardy, locking assertion failure when running netbeans

Binary package hint: sun-java6-jdk

Here's how it looks when I run netbeans 6.0 from the terminal:

% apps/netbeans-6.0/bin/netbeans
Locking assertion failure. Backtrace:
#0 /usr/lib/libxcb-xlib.so.0 [0xb4064767]
#1 /usr/lib/libxcb-xlib.so.0(xcb_xlib_unlock+0x31) [0xb40648b1]
#2 /usr/lib/libX11.so.6(_XReply+0xfd) [0xb40b929d]
#3 /usr/lib/jvm/java-6-sun-1.6.0.04/jre/lib/i386/xawt/libmawt.so [0xb41c88ce]
#4 /usr/lib/jvm/java-6-sun-1.6.0.04/jre/lib/i386/xawt/libmawt.so [0xb41a5067]
#5 /usr/lib/jvm/java-6-sun-1.6.0.04/jre/lib/i386/xawt/libmawt.so [0xb41a5318]
#6 /usr/lib/jvm/java-6-sun-1.6.0.04/jre/lib/i386/xawt/libmawt.so(Java_sun_awt_X11GraphicsEnvironment_initDisplay+0x2f) [0xb41a561f]
#7 [0xb5b52e9d]
#8 [0xb5b4bedd]
#9 [0xb5b4bedd]
#10 [0xb5b49249]
#11 /usr/lib/jvm/java-6-sun-1.6.0.04/jre/lib/i386/client/libjvm.so [0x621c40d]
#12 /usr/lib/jvm/java-6-sun-1.6.0.04/jre/lib/i386/client/libjvm.so [0x6310378]
#13 /usr/lib/jvm/java-6-sun-1.6.0.04/jre/lib/i386/client/libjvm.so [0x621c2a0]
#14 /usr/lib/jvm/java-6-sun-1.6.0.04/jre/lib/i386/client/libjvm.so(JVM_DoPrivileged+0x363) [0x6272153]
#15 /usr/lib/jvm/java-6-sun-1.6.0.04/jre/lib/i386/libjava.so(Java_java_security_AccessController_doPrivileged__Ljava_security_PrivilegedAction_2+0x3d) [0xb7b6496d]
#16 [0xb5b52e9d]
#17 [0xb5b4bd77]
#18 [0xb5b49249]
#19 /usr/lib/jvm/java-6-sun-1.6.0.04/jre/lib/i386/client/libjvm.so [0x621c40d]
Locking assertion failure. Backtrace:
#0 /usr/lib/libxcb-xlib.so.0 [0xb4064767]
#1 /usr/lib/libxcb-xlib.so.0(xcb_xlib_lock+0x2e) [0xb406481e]
#2 /usr/lib/libX11.so.6 [0xb40b85f8]
#3 /usr/lib/libX11.so.6(XGetVisualInfo+0x26) [0xb40af186]
#4 /usr/lib/jvm/java-6-sun-1.6.0.04/jre/lib/i386/xawt/libmawt.so [0xb41a4319]
#5 /usr/lib/jvm/java-6-sun-1.6.0.04/jre/lib/i386/xawt/libmawt.so [0xb41a4565]
#6 /usr/lib/jvm/java-6-sun-1.6.0.04/jre/lib/i386/xawt/libmawt.so [0xb41a53c9]
#7 /usr/lib/jvm/java-6-sun-1.6.0.04/jre/lib/i386/xawt/libmawt.so(Java_sun_awt_X11GraphicsEnvironment_initDisplay+0x2f) [0xb41a561f]
#8 [0xb5b52e9d]
#9 [0xb5b4bedd]
#10 [0xb5b4bedd]
#11 [0xb5b49249]
#12 /usr/lib/jvm/java-6-sun-1.6.0.04/jre/lib/i386/client/libjvm.so [0x621c40d]
#13 /usr/lib/jvm/java-6-sun-1.6.0.04/jre/lib/i386/client/libjvm.so [0x6310378]
#14 /usr/lib/jvm/java-6-sun-1.6.0.04/jre/lib/i386/client/libjvm.so [0x621c2a0]
#15 /usr/lib/jvm/java-6-sun-1.6.0.04/jre/lib/i386/client/libjvm.so(JVM_DoPrivileged+0x363) [0x6272153]
#16 /usr/lib/jvm/java-6-sun-1.6.0.04/jre/lib/i386/libjava.so(Java_java_security_AccessController_doPrivileged__Ljava_security_PrivilegedAction_2+0x3d) [0xb7b6496d]
#17 [0xb5b52e9d]
#18 [0xb5b4bd77]
#19 [0xb5b49249]

Netbeans still runs fine, thanks to a tip I found somewhere:
This is in my .zshrc:
export LIBXCB_ALLOW_SLOPPY_LOCK=true

All other java-programs also output funky error-messages like these.
Cgoban3, another java-program, won't start without the LIBXCB_ALLOW_SLOPPY_LOCK export.

My kernel:
2.6.24-5-generic

Xorg.0.log seems fine, but I can attach it anyways.

Java:
ii sun-java6-jdk 6-04-0ubuntu1 Sun Java(TM) Development Kit (JDK) 6