Attaching an Emitter to Match Move

Hi,

I'm constantly failing to attach an Emitter to a Motion Tracker as a background.

Here's what I did:

1. I created a tracker on my video using "Analyze Motion".
2. I created a group containing a 3D object, added the "Match Move" behaviour, reviewed it and it works just fine.
3. Then I added the default Plazma Orb from the Library to the timeline which created a new group.
4. I added the "Match Move" behaviour to the Plazma Orb Group and selected the analyzed motion.

Now the 3D object is following the motion track perfectly. The Orb, which should nicely sit behind it, just doesn't. It sometimes jumps away from the track or does other funny things.

I just can't figure it out. All I want to achieve is a moving circle shaped foggy background that sits behind my 3D object and moves with it in a centered way.

Can anyone help me?

Thanks, Alex