I had this happened before, but this time I can reproduce this bug with success. As seen on the video:
http://www.youtube.com/watch?v=wTty37QXvxU
If you walk backwards in crouch position with pistol in your hands over certain areas (of grass?) on Stratis at default compound at [2464.14,5685.74,0.00136566], you get what might seem like a strange dust effect and FPS goes to the dogs (as you can see from hint).
This reminds me of dust effect on tracks of paradroping vehicles bug on dedicated server while they are still in the air.