Experimenting, I placed two JPGs on the timeline and applied Fades > Effect fades > Particle. Then I deleted the sound effect in track 6. To my surprise, the video effect disappeared too! It was replaced by the standard Crossfade.
Same with the other 'Effect fades' I tried.
Or for better quality: https://dl.dropboxusercontent.com/u/4019461/MEP-FadesPuzzle.jpg
I'm curious how that's possible? The work-arounds were to either reduce its volume or duration to zero. But in practice I may also have other material on track 6 at that position, complicating things.