I have created a symbol in illustrator CS5 and then, export it in my library in Flash CS5 with the scale-9. The symbol is composed of a rectangle and a logo (group of path). The logo is on the right of the symbol. That's why I have placed the scale-9 about in the center. In this way, the logo is not deformed, just the rectangle.Then, I have exported the file to SWF.
But by loading the symbol in Flex, the scale-9 is correctly applied except on the logo. The logo is deformed and not the rest.