Java EE (Java Enterprise Edition) General Discussion

I've recently been developing an application that relys on a JMS Provider to route messages to peers. The application must have the ability to disconnect and reconnect to the JMS Provider, and it must queue messages if the JMS Provider goes down or is not immediately available. I experimented with the Sun J2EE 1.3.1 reference implemention, it worked great as long as the j2ee server stayed up, kill the j2ee server and my clients would never reconnect. So I tried OpenJMS (using the EXACT same code as I did with the J2EE Provider) and it works perfectly. If the OpenJMS Server goes down my clients queue up outgoing messages, restart the OpenJMS Server and the clients reconnect and forward. So what's up with the J2EE JMS Provider? I assumed that it would be the most robust of them all.