From "https://github.com/SpringSource/spring-integration/wiki/Spring-Integration-2.0-to-2.1-Migration-Guide":
keep-released-messages (both aggregator and resequencer) - Will store messages after their release. Mainly used for monitoring purposes. Default is 'true'

Out of curiosity I wanted to test the keep-released-messages attribute on the aggregator, using spring-integration-2.1.0.RELEASE. (from maven...)

<dependency>
<groupId>org.springframework.integration</groupId>
<artifactId>spring-integration-core</artifactId>
<version>2.1.0.RELEASE</version>
<type>jar</type>
</dependency>


The xsd seems fine, and my IDE autocompletes the keep-released-messages attribute, buit my log confronts be with this.:

Code:
Context initialization failed
org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'org.springframework.integration.aggregator.AggregatingMessageHandler#0': Error setting property values; nested exception is org.springframework.beans.NotWritablePropertyException: Invalid property 'keepReleasedMessages' of bean class [org.springframework.integration.aggregator.AggregatingMessageHandler]: Bean property 'keepReleasedMessages' is not writable or has an invalid setter method. Does the parameter type of the setter match the return type of the getter?
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.applyPropertyValues(AbstractAutowireCapableBeanFactory.java:1361)
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1086)
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:517)
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:456)
	at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:293)
	at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:222)
	at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:290)
	at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:192)
	at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:585)
	at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:895)
	at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:425)
	at org.springframework.web.context.ContextLoader.createWebApplicationContext(ContextLoader.java:276)
	at org.springframework.web.context.ContextLoader.initWebApplicationContext(ContextLoader.java:197)
	at org.springframework.web.context.ContextLoaderListener.contextInitialized(ContextLoaderListener.java:47)
	at org.apache.catalina.core.StandardContext.listenerStart(StandardContext.java:4723)
	at org.apache.catalina.core.StandardContext$1.call(StandardContext.java:5226)
	at org.apache.catalina.core.StandardContext$1.call(StandardContext.java:5221)
	at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:303)
	at java.util.concurrent.FutureTask.run(FutureTask.java:138)
	at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
	at java.lang.Thread.run(Thread.java:619)
Caused by: org.springframework.beans.NotWritablePropertyException: Invalid property 'keepReleasedMessages' of bean class [org.springframework.integration.aggregator.AggregatingMessageHandler]: Bean property 'keepReleasedMessages' is not writable or has an invalid setter method. Does the parameter type of the setter match the return type of the getter?
	at org.springframework.beans.BeanWrapperImpl.setPropertyValue(BeanWrapperImpl.java:1052)
	at org.springframework.beans.BeanWrapperImpl.setPropertyValue(BeanWrapperImpl.java:921)
	at org.springframework.beans.AbstractPropertyAccessor.setPropertyValues(AbstractPropertyAccessor.java:76)
	at org.springframework.beans.AbstractPropertyAccessor.setPropertyValues(AbstractPropertyAccessor.java:58)
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.applyPropertyValues(AbstractAutowireCapableBeanFactory.java:1358)
	... 21 more