Cannot use the "@extend .spanN;" within a media query in this version and future version of Sass.

TB Broke.scss

.main-content {
  @extend %container-fluid;
  
  .content {
    @extend .row-fluid;  
  }
  .sidebar {
    @include respond-to(47em) {
      float: left;
      @extend .span3; // Cannot use this type of @extend within a media query
    }
  } //sidebar

  .main-article {
    @include respond-to(47em) {
      float: left;
      @extend .span8;   // Cannot use this type of @extend within a media query
      @extend .offset1; // Cannot use this type of @extend within a media query
    }
  } //main-article
} //main-content