Resizing a vectorobject without blurrying vertical lines

Right… I can’t help feeling ashamed for actually having to ask…
so every suggestion would be immensely appreciated.

Okay, here’s the deal.

I have a square with an outline & filled with a color and inside that square there is another square, just outlines, no fill.

Since i hadn’t made up the exact shape yet, it now consists of
1 bg colored square (graphic symbol), and all the sides of the outlines are left, right, up and down squares (graph. symbols) of 1 pixel width (for left & right) and 1 pixel height (for up and down obviously). I elaborate on this, because maybe here I am doing something wrong.

Okay, now with a motion tween (since it is grouped as a symbol now) I want to scale it wider.

But here comes the catch. Despite the fact that all the symbols are positioned on whole numbers (so x=100 y=100) and the size of the objects are also whole numbers), when I resize it, for some reason the lines blur when the swf is published (a screendump + zoom in Photoshop confirmed what I already thought to see).

= But how is this possible, that despite being positioned at the correct coordinates, it still blures???

so basically, how can I keep my vertical lines from stretching, while only the horizontals and backgrounds do scale?