Btw, why isn't is completely symmetrical?
It's the encoded data. It requires a transparent border that is one-pixel thick. In that border, black lines describe how it is to be used. The black line on the top and left show which part of the texture is to be stretched. Selba Ward's version doesn't make use of the right and bottom lines, which describe where content should go, although I will be adding a way to retrieve that information.
The black lines don't have to be two-pixels (or more) long, they can be just a single pixel!
My version has the added bonus that if no black lines (guides) are present, the entire image is stretched to match the given size. Can be useful if you need to rescale to a specific size rather than scale.
Have a look at my previous post. I edited it to show my version of your texture in use!
EDIT: For more information on the 9patch and a view of what the black lines look like on all four sides, see
this article.