Write a class that:

1. obtains the WebLogic TM
2. starts a txn
3. registers a Synchronization
4. attempts to commit the txn
5. have your Synchronization throw an exception in its beforeCompletion

Do you get back your original exception as part of the exception hierarchy that comes back from WebLogic? If so, as a proof try the following:

1. obtains the WebLogic TM
2. starts a txn
3. registers a Synchronization
4. attempts to commit the txn
5. have your Synchronization mark the transaction for rollback only
6. have your Synchronization throw an exception in its beforeCompletion

Do you now get the same situation as you reported here initially?