Interesting.
Not something I've seen myself, but I wonder if it has something to do with the suppression of image processing during saccadic movement. Your visual cortex shuts down for a tenth of a second or so while you shift your gaze (otherwise you'd see a rapid lurch in your visual field). It backfills the gap with a static "frame" from your new fixation point. So I'm wondering if what you're noticing is that static tenth of a second.

Some more, related, visual tricks:
You can detect the visual processing shutdown by looking at yourself in a mirror and shifting your gaze from the reflection of one eye to the other. You can't see your own eyes move, despite the fact that you can see movement very readily in another person.
And you can detect the backfill, although not predictably, by glancing at a watch with a sweep second-hand. Most people have had the sensation of looking at a watch and thinking it has stopped, only to see the second-hand make a tick after what seems longer than a second. What's happened is you've caught the second-hand just after a movement, and the sensory backfill in consciousness has prolonged the apparent gap before the next tick.

Grant Hutchison