Do you ever experience issues with display flickering due to two surfaces being close to each other?
In the image to the below (Figure 1), the rear light and fuel filler door suffer from this problem of display. This is just a floating z clip plane issue. If you rotate the scene so you're looking at it straight from the side the problem goes away.
Figure 1: ZBuffer or Zclip Issues with Image Quality.
When you put the scene such that the particle traces are flowing back towards the viewer the z-clip planes get adjusted to attempt not to clip them off.
In Figure 2, you can also see that when we turn off the particle traces, the problem goes away (the Z-clip buffer results itself since the particle traces are not being drawn.
Figure 2: No Zbuffer or Zclip Issues without Particle Traces.
So what's happening is that you're loosing a bunch of z resolution in the area of the coincident surfaces, resulting in this inability to correctly draw the “top” or “front” surface.
How to Improve this? You can adjust the Z-clip options to improve this situation.
Method 1: Turn off the streamlines (the z-clip buffer is correctly set). Open up the Z-Clip Transformation Editor, and UnCheck the “Float z-clip planes with transforms”. This will freeze the z-buffer, and when you turn on the particle Traces, everything remains correctly drawn.
Method 2: Fix the minimum z-value in the Z-Clip dialog to a fixed value (1 in this case works great.
The Image below (Figure 3), is now correctly drawn with particle traces.