a bug about parse scss

[chenxiaochun]

the scss code

@mixin ico-common($imgUrl){
    display: inline-block;
    background: url(i/$imgUrl);
    background-repeat: no-repeat;
}

@mixin ico-size($width,$height){
    width: $width;
    height: $height;
}

.test{
    @include ico-common("icon.png");

    @include ico-size(100px, 100px);
}

the css code

.test {
  display: inline-block;
  background: url(i/$imgUrl);
  background-repeat: no-repeat;
  width: 100px;
  height: 100px; }

The "$imgurl" can not parsed.