There's a certain "bug", if you will, in Flash that incorrectly handles transparency of alpha blended clips when more than so many of these clips are layed on top of one another. What happens is Flash mistakenly applies transparency through an underlying solid movieclip when a series of movieclips with transparency applied are layered above it. Here, there are two solid clips the size of the screen, one orange, the other blue. Only the blue clip is visible at first, completely hiding the orange one. However, as other smaller clips with a low set alpha are randomly placed above this blue clip, you can start to see the orange come through as Flash reveals it from under the blue clip.
