Question about visual artifacts - may be stuttering

[RiverC]

I've noticed some visual artifacts in my rendering. It's not tearing (I think I tackled that before) but is probably what is called 'stuttering'. In short, it is an effect where if you move quickly enough you can see 'trails' of previous frames (perhaps frames between frames?) and it is most noticeable with textures that are effectively black (due to lighting or just using black in the image file itself.)

Is this:

1. An openGL settings issue, where some differing values need to be set on glBlendFunc
2. An openGL issue with fragments that are actually black (0.0,0.0,0.0,1.0)
3. A sync issue relating to my two video cards - though I don't see it in other 3d games like Minecraft
4. A sync issue relating to uneven frame calculation - LWJGL's FPS even with vsync + Display.sync in windowed mode is not exactly even
5. A problem relating to my two-monitor setup - though again, no issues with other games
6. A problem relating to windowed rendering itself - though again, no issues with other games
7. Something that always happens *in your brain* but is only really noticeable when you've got pure black on the screen?

I stuck my nose around a lot of threads, but the issue I get, unlike some stuttering, is not 'once or twice a second' but a continuous 'motion blur' that I see. If I take a screenshot it looks okay, so I might need to use my SLR to capture a frame to see if it's not the soft machine's features.

UPDATE:

A quick shot with my CANON shows a trail of not just one frame, but two... I'm suspecting I'm calling some function too many times, but how to know which one!

UPDATE x2:

Absurdly large picture of the actual effect, as taken by my SLR:



UPDATE x3:

Turning off lighting entirely seems to remove this effect. I'll have to investigate my lighting shaders to see if they're the culprit in this madness.