Simon,

The problem is being caused by you importing a swf animation into Flash. A swf file is the output of Flash. It is not intended to be IMPORTED to Flash. To import an animation to Flash you need the .fla file that holds the tween information.

That said however, swf is an excellent medium for bringing non-animated objects from Xtreme to Flash. I would recommend you use swf4 for this transfer as later swf versions can also have strange effects.