Per Ales:

This one

• http://hudson.qa.jboss.com/hudson/view/JBoss%20AS/job/JBoss-AS-6.0.x-testSuite-sun16/lastCompletedBuild/testReport/org.jboss.test.isolation.test/JavaClassIsolationUnitTestCase/testJavaClassIsNotLoadedFromIsolatedClassLoader/
  looks somehow expected, but the behavior changed a bit.

We explicitly build "illegal" resources

<!-- build test-java-class-isolation.sar -->
<mkdir dir="${build.resources}/isolation/java/org/jboss/test"/>
<copy file="${build.classes}/org/jboss/test/isolation/mbean/JavaClassIsolationMBean.class"
tofile="${build.resources}/isolation/java/org/jboss/test/Test.class"/>

<mkdir dir="${build.resources}/isolation/java/rmi/registry"/>
<copy file="${build.classes}/org/jboss/test/isolation/mbean/JavaClassIsolationMBean.class"
tofile="${build.resources}/isolation/java/rmi/registry/Registry.class"/>

<jar destfile="${build.lib}/test-java-class-isolation.sar">
<fileset dir="${build.classes}">
<include name="org/jboss/test/isolation/mbean/**"/>
</fileset>
<fileset dir="${build.resources}/isolation/">
<include name="META-INF/*.xml"/>
<include name="java/**"/>
</fileset>
</jar>

only to test them here

public void test() throws Exception
{
// Use our scoped classloader
ClassLoader cl = getClass().getClassLoader();

// Should be able to find the class as a resource
URL resource = cl.getResource("java/org/jboss/test/Test.class");
if (resource == null)
throw new RuntimeException("Unable to find resource java/org/jboss/test/Test.class");

// Should not be able to load the resource
try

{ cl.loadClass("java.org.jboss.test.Test"); throw new RuntimeException("Should not be able to load class"); }

catch (ClassNotFoundException expected) // HERE — we get security exception now instead

{ // Should not be able to load it log.info("Got expected exception", expected); }

// Should be able to load the resgistry class even though it is in our deployment
cl.loadClass("java.rmi.registry.Registry");
}

resulting in

DEPLOYMENTS IN ERROR:
Deployment "vfs:///qa/services/hudson/hudson_workspace/workspace/JBoss-AS-6.0.x-testSuite-sun16/JBossAS/testsuite/output/lib/test-java-class-isolation.sar" is in error due to the following reason(s): java.lang.SecurityException: Prohibited package name: java.org.jboss.test

The question is what was changed in our CL layer.