Bitmaps not scaling correctly AS3

Question

I was experimenting with bitmaps and created an alpha mask. When i test the program in full screen, it works fine however when I re-size the screen, the bitmap alpha masks doesn't seem to scale correctly. Below are illustrations of my issue. The bitmap alpha mask is shown as a purple background for visibility, and the blue portion is where the bitmap is completely transparent.

Full Screen (Looks Good)

Regular Screen (Looks like the mask is shifted to the left):

Why is this happening and what can i do to fix it? Thank you.

Answer 1

It turns out the text box Anti-aliasing was the problem. I changed the ani-aliasing from "Anti-alias for readability" to "Anti-alias for animation" and now everything scales properly.