Section 3.4.8 of the EJB 3.1 Spec:
By default, session bean invocations through the Remote, Local, and no-interface views are synchronous. The client blocks for the duration of the invocation and is returned control only after all invocation processing has completed. Clients can achieve asynchronous invocation behavior by invoking
session bean methods that have been designed to support asynchrony.
When a client invokes an asynchronous method, the container returns control to the client immediately
and continues processing the invocation on a separate thread of execution.
If it's not running in a different thread, that would be a bug in AS7, unless AS7 isn't providing it because it's not required in EJB 3.1 Lite. At this point your best bet is to use JMS (if you're in AS7, you'll have to use the preview profile to get JMS support).
It does seem like a bug with AS7. Does anyone know when AS7 would support async?