Long running tasks - CDI issues?

Hi!

I have probably not the simplest setup running on my Vaadin 6.7.8 application:

The main application class is @Stateful and so injected using InitialContext lookup in getNewApplication(HttpServletRequest request)
This application further then uses a subclassed Vaadin Panel, having a TabSheet. One of the tabs then contains another subclassed Vaadin Panel, from where I can trigger a long running task.
So far so good. I am using Vaadin ProgressIndicator, which properly shows the progress aso...

Now the problem: When the calculation finishes, I need to pass its result back to the Panel - but I cant that get to work.
From within the long running thread, the result is okay, I checked that. But whenever/however I give that result (List<String>) back to the Vaadin hierarchy, the passed result list is null on the other end of the "tunnel" (any Vaadin component).
I tried approx. 10 different ways to pass my result from the Thread back to the application/Vaadin components, but struggled all the way. Any help/hints appreciated!!

TIA