It's a quite annyoing bug. Or is there any workaround for this?
I guess what you call a bug, they call that "as designed", since that "first image" of a png overlay sequence is no more than the flattened background you have when no interaction started, and that is not removed when this particular interaction starts. From here, i tend to put no first image and have my sequence auto start (even with a delay if necessary).
that was exactly the same workaround I used. Weather it is "by design" or not...it makes not really sense especially with transparent PNGs.