Limited number of PNG imports retain transparency

Anybody seen this issue before? I have 15 .png files (layer exports from Photoshop) that have been distributed to separate layers and defined as movieclips so I can perform some alpha operations, masking, etc. on them. When the 13th one is imported to stage, .png number 1 dissappears! If I import another one, .png number two dissapears as well, and so on. I am not aware of any limit to the number of stacked transparent .png’s, and am running MX 2004 Pro. Known issue? I searched all over for it and couldn’t find anything.
With 13 .png’s on the stage, if I hide any of the layers then the bottom .png becomes visible again. help!
.fla here