IllegalAccessError for Package-Scope-Interfaces

When you declare a Interface to be accessible only inside a package and setup a proxy in a test using a parallel package hierarchy, the proxy throws a IllegalAccessError on the first call:

java.lang.IllegalAccessError: tried to access class plugin.operation.cleanup.IElementCleanup from class $Proxy2
at $Proxy2.createCleanup(Unknown Source)
at ModelCleanUp.cleanupAndValidate(ModelCleanUp.java:35)
at plugin.operation.cleanup.ModelCleanUpTest.test_validateAndCleanup(ModelCleanUpTest.java:56)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:585)
at junit.framework.TestCase.runTest(TestCase.java:168)
at junit.framework.TestCase.runBare(TestCase.java:134)
at junit.framework.TestResult$1.protect(TestResult.java:110)
at junit.framework.TestResult.runProtected(TestResult.java:128)
at junit.framework.TestResult.run(TestResult.java:113)
at junit.framework.TestCase.run(TestCase.java:124)
at junit.framework.TestSuite.runTest(TestSuite.java:232)
at junit.framework.TestSuite.run(TestSuite.java:227)
at org.junit.internal.runners.OldTestClassRunner.run(OldTestClassRunner.java:76)
at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:45)
at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:460)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:673)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:386)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:196)

interface IElementCleanup {
public boolean createCleanup(IElement element);
}

@Test
@Test
public void test_validateAndCleanup()