Css concatenation breaks paths if concatenated css is at a different path to source css.

[edeustace]

If you have a folder like:

/css
  one.css
  two/
    two.css
    img.png

and in two.css you have:

.style {
  background-image: url('img.png')
}

After concatenation the css will break because it's trying to load 'img.png' from a file called: css/css-1111.css.

That is - the paths aren't maintained.