Spring Cache Abstraction VS interfaces VS key param (“Null key returned for cache operation” error)

While implementing, I came across a problem with Spring Cache Abstraction VS interfaces.
Lets say I have the following interface:

package com.example.cache;

public interface IAddItMethod 
{   
    Integer addIt(String key);
}

And the two following implementations:

package com.example.cache;

import org.springframework.cache.annotation.Cacheable;
import org.springframework.stereotype.Component;

@Component
public class MethodImplOne implements IAddItMethod 
{
    @Override
    @Cacheable(value="integersPlusOne", key="#keyOne")
    public Integer addIt(String keyOne) 
    {
        return new Integer(Integer.parseInt(keyOne) + 1);
    }
}

.

package com.example.cache;

import org.springframework.cache.annotation.Cacheable;
import org.springframework.stereotype.Component;

@Component
public class MethodImplTwo implements IAddItMethod 
{
    @Override
    @Cacheable(value="integersPlusTwo", key="#keyTwo")
    public Integer addIt(String keyTwo)
    {
        return new Integer(Integer.parseInt(keyTwo) + 2);
    }
}

Note that the IAddItMethod is not the one specifying @Cacheable. We could have other implementation (ex MethodImplThree) without the @Cacheable annotation.

We’ve got a simple beans.xml with:

context:component-scan base-package="com.example.cache"

Adding to that, two jUnit test cases:

package com.example.cache;

import static org.junit.Assert.assertEquals;

import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Qualifier;
import org.springframework.test.context.ContextConfiguration;
import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;

@RunWith(SpringJUnit4ClassRunner.class) 
@ContextConfiguration(locations = {"classpath:beans.xml"})  
public class MethodImplOneTest 
{

    @Autowired
    @Qualifier("methodImplOne")
    private IAddItMethod classUnderTest;

    @Test
    public void testInit() 
    {
        int number = 1;
        assertEquals(new Integer(number + 1), classUnderTest.addIt("" + number));
    }

}

.

package com.example.cache;

import static org.junit.Assert.assertEquals;

import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Qualifier;
import org.springframework.test.context.ContextConfiguration;
import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;

@RunWith(SpringJUnit4ClassRunner.class) 
@ContextConfiguration(locations = {"classpath:beans.xml"})  
public class MethodImplTwoTest 
{

    @Autowired
    @Qualifier("methodImplTwo")
    private IAddItMethod classUnderTest;

    @Test
    public void testInit() 
    {
        int number = 1;
        assertEquals(new Integer(number + 2), classUnderTest.addIt("" + number));
    }

}

When I run the tests individually, they succeed.
However, if I run them both together (selecting the package, right-click, run as), the second one (not necessarily MethodImplTwoTest, just the second one running) will fail with the following exception:

java.lang.IllegalArgumentException: Null key returned for cache operation (maybe you are using named params on classes without debug info?) CacheableOperation[public java.lang.Integer com.example.cache.MethodImplOne.addIt(java.lang.String)] caches=[integersPlusOne] | condition='' | key='#keyOne'
    at org.springframework.cache.interceptor.CacheAspectSupport.inspectCacheables(CacheAspectSupport.java:297)
    at org.springframework.cache.interceptor.CacheAspectSupport.execute(CacheAspectSupport.java:198)
    at org.springframework.cache.interceptor.CacheInterceptor.invoke(CacheInterceptor.java:66)
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:172)
    at org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:202)
    at $Proxy16.addIt(Unknown Source)
    at com.example.cache.ITMethodImplOneIntegrationTest.testInit(ITMethodImplOneIntegrationTest.java:26)
    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:597)
    at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:45)
    at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:15)
    at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:42)
    at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:20)
    at org.springframework.test.context.junit4.statements.RunBeforeTestMethodCallbacks.evaluate(RunBeforeTestMethodCallbacks.java:74)
    at org.springframework.test.context.junit4.statements.RunAfterTestMethodCallbacks.evaluate(RunAfterTestMethodCallbacks.java:83)
    at org.springframework.test.context.junit4.statements.SpringRepeat.evaluate(SpringRepeat.java:72)
    at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.runChild(SpringJUnit4ClassRunner.java:231)
    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:47)
    at org.junit.runners.ParentRunner$3.run(ParentRunner.java:231)
    at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:60)
    at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:229)
    at org.junit.runners.ParentRunner.access$000(ParentRunner.java:50)
    at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:222)
    at org.springframework.test.context.junit4.statements.RunBeforeTestClassCallbacks.evaluate(RunBeforeTestClassCallbacks.java:61)
    at org.springframework.test.context.junit4.statements.RunAfterTestClassCallbacks.evaluate(RunAfterTestClassCallbacks.java:71)
    at org.junit.runners.ParentRunner.run(ParentRunner.java:300)
    at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.run(SpringJUnit4ClassRunner.java:174)
    at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:50)
    at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:467)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:683)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:390)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:197)

note: I'm using Eclipse STS 3.0 and the "Add variable attributes to generated class files" is enabled.

IMPORTANT: If I don't specify the "key" in the @Cacheable annotations, it works.

Is there anything I forgot to specify? config? annotations?

Thanks in advance!