Oh, I was meaning to file something like this.
I *think* this is because MMV preloads the previous and next image at the same time as loading the current one. I haven't had time to verify this by looking at the code yet, though.
Whoa that was slow.
Bartosz: the prev/next image should only start loading when the current one has finished, although the way that is implemented is not perfect (e.g. the API request for the image metadata might start sooner).
This could also be caused by thumbnail rendering times, since the original image is huge.