7.2. Container invocations and interception states:
When the container invokes a method of a bean, the invocation may or may not be treated as a business method invocation:

• Invocations of message listener methods of message-driven beans during message delivery are business method invocations.

As MDBs are not CDI beans their methods shouldn't be business invocations (and thus should not pass through method interceptors and decorators).

If the original intent was to support such use case the spec should be reworded.