FULL PRODUCT VERSION :
java version "1.8.0_51"
Java(TM) SE Runtime Environment (build 1.8.0_51-b16)
Java HotSpot(TM) Client VM (build 25.51-b03, mixed mode)

ADDITIONAL OS VERSION INFORMATION :
Windows Vista Enterprise (6002: SP2)
Windows 7 - 64bit Enterprise (7601: SP1)

EXTRA RELEVANT SYSTEM CONFIGURATION :
system integration java 1.8.0_51
Webstart enabled java versions: 1.6.0_43, 1.7.0_17, 1.7.0_45, 1.7.0_72
separate company signature on cacert keystore

A DESCRIPTION OF THE PROBLEM :
a java applet to start on jre 1.6.0_43 over Java Webstart (Java 8 u 51) is broken:

here a simple test system with this szenario:
- start as Applet on WebSite with JNLP: ok
- start as Application with JNLP: error ... ClassNotFoundException: GetJavaVersion
java.lang.ClassNotFoundException: GetJavaVersion
at sun.plugin2.applet.Plugin2ClassLoader$2.run(Unknown Source)
at sun.plugin2.applet.Plugin2ClassLoader$2.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at sun.plugin2.applet.Plugin2ClassLoader.findClassHelper(Unknown Source)
at sun.plugin2.applet.JNLP2ClassLoader.findClass(Unknown Source)
at sun.plugin2.applet.Plugin2ClassLoader.loadClass0(Unknown Source)
at sun.plugin2.applet.Plugin2ClassLoader.loadClass(Unknown Source)
at sun.plugin2.applet.Plugin2ClassLoader.loadClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at sun.plugin2.applet.Plugin2ClassLoader.loadCode(Unknown Source)
at sun.plugin2.applet.Plugin2Manager.initAppletAdapter(Unknown Source)
at sun.plugin2.applet.Plugin2Manager$AppletExecutionRunnable.run(Unknown Source)
at java.lang.Thread.run(Unknown Source)

- start as Application from command line: <pathJre16043>java.exe -jar GetJavaVersion ... ok
- start as Application from command line: <pathJre16043>java.exe -cp GetJavaVersion GetJavaVersion ... ok
(jar format is compatible)

broken only on application (applet) start over webstart.
with a jre version 1.7.0_17 as runtime for application i don't error on this jnlp and jar.
on jre 1.7.0_72 as systemintegrated java version, the applet start as application over webstart on java 1.6.0_43



REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------
--- FILE:GetJavaVersion.java ---

import java.applet.*;
import java.awt.*;
import javax.swing.*;
import java.net.*;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;

public class GetJavaVersion extends Applet
{
  private static String getVersion()
    throws Exception
  {
    String Ver = "";
    try{
      Ver = System.getProperty("java.version");
    }
    catch(Exception e){
      throw new Exception( e);
    }
    return Ver;
  }
  
  private static String getVendor()
    throws Exception
  {
    String Ven = "";
    try{
      Ven = System.getProperty("java.vendor");
    }
    catch( Exception e){
      throw new Exception( e);
    }
    return Ven;
  }
  
  public void init() {
    String ven = "";
    String ver = "";
    Exception eVen = null;
    Exception eVer = null;

    try {
      ven = getVendor();
    }
    catch( Exception e) {
      eVen = e;
    }
    try {
      ver = getVersion();
    }
    catch( Exception e) {
      eVer = e;
    }

    if( eVer == null && eVen == null) {
 

      this.setBackground( Color.green);
    }
    else {
      this.setBackground( Color.red);
      if( eVen != null) { ven = eVen.toString(); }
      if( eVer != null) { ver = eVer.toString(); }
    }
    this.setLayout( new GridLayout( 2, 1));
    this.add( new Label( "Java Version: " + ver));
    this.add( new Label( "Vendor: " + ven));
  }

  public String getAppletInfo() {
    return "a test to get java version...";
  }

  public static void main( String[] args)
  {
    JFrame f = new JFrame( "GetJavaVersion Application");
    f.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE);
    GetJavaVersion me = new GetJavaVersion();

    me.init();
    me.start();

    f.add( "Center", me);

    

    f.setSize( 300, 80);
    f.setVisible( true);
  }
  
}


--- FILE: APPLICATION_TEMPLATE.JNLP ---
<?xml version="1.0" encoding="UTF-8"?>
<jnlp spec="1.0+" codebase="*">
  <information>
    <title>GetJavaVersion</title>
    <vendor>DB Systel GmbH</vendor>
  </information>
  <update check="always" policy="always" />
  <resources>
    <!-- Application Resources -->
    <j2se version="*"
          href="http://java.sun.com/products/autodl/j2se" />
    <jar href="GetJavaVersion.jar" main="true" />
  </resources>
  <applet-desc
     name="GetJavaVersion"
     main-class="GetJavaVersion"
     width="300"
     height="60" >
  </applet-desc>
</jnlp>

--- FILE: GetJavaVersion.jnlp (original a server script with dynamic java Version ---
<?xml version="1.0" encoding="UTF-8" ?>
<jnlp spec="1.0+" codebase="URL2SERVERWITHPATH">
  <information>
    <title>GetJavaVersion</title>
    <vendor>DB Systel GmbH</vendor>
  </information>
  <update check="always" policy="always" />
  <resources>
    <!-- Application Resources -->
    <j2se version="1.6.0_43"
          href="http://java.sun.com/products/autodl/j2se" />
    <jar href="GetJavaVersion.jar" main="true" />
  </resources>
  <applet-desc
    name="GetJavaVersion"
    main-class="GetJavaVersion"
    width="300"
    height="60" >
  </applet-desc>
</jnlp>
---------- END SOURCE ----------

SUPPORT :
YES