I was playing around with the particle Simulator in HF3 Pro. I wanted them to fly from behind the camera into the picture while they should be out of foucs for the first few seconds.
These two frames are right next to each other.
As you can see the the blur in the second frame is completly gone, while the blur in the first one is a bit strange too. In the third frame it comes back similar to the first one.
You can find the project file here: Buggy Project
CPU: Intel Core 2 Quad Q 9400
GPU: Nvidia GTX 470 with the lastest driver
RAM: 8 Gb
I hope this is enough information and its not caused by setting something up the wrong way.