Alpha transparency not working on PNGs

I'm currently constructing a scrollbar as part of a website using as3 and png images. I've got loaders for each image inside of an array, and when loading on each image finishes, it's added as a child to a sprite on the stage. I've got a background image with no transparency, which loads fine. On top of that, I've got the actual slider, which loads the RGB data, and appears to be using the alpha as a 1-bit mask. So anywhere that I have partial transparency, it just shows up as black, where it should be showing the background underneath. I can't find any attribute that will change the way loaded images process alpha transparency. Does anyone have a solution for this? Whatever knowledge you have on the issue would be much appreciated.

Thanks for your time,

-tjuicet