compact form for background is not handled

[riffraff]

input code

div.1 {
  background: url("img/1.png") center no-repeat;
}
div.2 {
  background: url(img/2.png) ;
}

produces an identical output code, whereas

div.1 {
  background: url("public/images/explore_all.png");
}
div.2 {
  background: url(public/images/explore_places.png) ;
}

produces an expected output of

div.1 {
  background: url('img/images.png') no-repeat 0 0;
}
div.2 {
  background: url('img/images.png') no-repeat -54px 0;
}

IMO spritemapper should at least report "unsupported xxx" in cases such as this, if it cannot support it better.

[sairam]

Are sprites not supported on compact form backgrounds ?