MovieClips showing when swf opens

Here’s a little something I made from kirupa’s very basic tutorial on Classes and Movie Clips. [URL=“http://megaswf.com/serve/1159253”]Colorful Circles.

When you see the file you’ll see all the circles and back added once and then disappear. I just have two straightforward questions regarding this.

1> Why does it happen?
2> How can I get rid of it?