plugin crashes with NullPointerException on minecraft classic

[wdesmet]

When trying to load this page:
http://www.minecraft.net/play.jsp

I get the following in .xsession-errors:

java version "1.6.0_20"
OpenJDK Runtime Environment (IcedTea6 1.9.7) (6b20-1.9.7-0ubuntu1)
OpenJDK 64-Bit Server VM (build 19.0-b09, mixed mode)
java.lang.NullPointerException
        at sun.applet.PluginAppletViewer.handleMessage(PluginAppletViewer.java:649)
        at sun.applet.PluginStreamHandler.handleMessage(PluginStreamHandler.java:270)
        at sun.applet.PluginMessageHandlerWorker.run(PluginMessageHandlerWorker.java:82)
java.lang.RuntimeException: Failed to handle message: width 854 height 480 for instance 2
        at sun.applet.PluginAppletViewer.handleMessage(PluginAppletViewer.java:660)
        at sun.applet.PluginStreamHandler.handleMessage(PluginStreamHandler.java:270)
        at sun.applet.PluginMessageHandlerWorker.run(PluginMessageHandlerWorker.java:82)
Caused by: java.lang.NullPointerException
        at sun.applet.PluginAppletViewer.handleMessage(PluginAppletViewer.java:649)
        ... 2 more

ProblemType: Bug
DistroRelease: Ubuntu 10.10
Package: icedtea6-plugin 6b20-1.9.7-0ubuntu1
ProcVersionSignature: Ubuntu 2.6.35-28.50-generic 2.6.35.11
Uname: Linux 2.6.35-28-generic x86_64
NonfreeKernelModules: fglrx
Architecture: amd64
Date: Tue Apr 19 19:36:37 2011
InstallationMedia: Ubuntu 10.04 LTS "Lucid Lynx" - Release amd64 (20100429)
ProcEnviron:
 LANGUAGE=en
 PATH=(custom, user)
 LANG=nl_BE.utf8
 SHELL=/bin/bash
SourcePackage: openjdk-6