Sourcemap wrong filename

Question

I have an issue with my gulpfile.js when generating sourcemaps for my sass. When I use Developer Tools to inspect an element it's source is shown as _box-sizing.scss when it's true source is _header.sass.

Here's an extract from my gulpfile.js

var options = {
    styles: {
        "source": "public/sass/main.sass",
        "destination": "public/css",
        "sourcemaps": "sourcemaps",
        "sourceRoot": "../../sass/"
    }
}

gulp.task('styles', function() {
    return sass(options.styles.source, {sourcemap: true, style: 'compressed'})
        .on('error', function(err) { console.error('Error!', err.message); })
        .pipe(prefix("last 1 version", "> 1%", "ie 8", "ie 7"))
        .pipe(sourcemaps.write(options.styles.sourcemaps, {includeContent: false, sourceRoot: options.styles.sourceRoot}))
        .pipe(gulp.dest(options.styles.destination));
});

This generates a sourcemap in public/css/sourcemaps. The sourceMappingURL in my .css file reads /*# sourceMappingURL=sourcemaps/main.css.map */

Which looks like this

{  
   "version":3,
   "sources":[  
      "main.css",
      "import/lib/_normalize.scss",
      "import/lib/neat/grid/_box-sizing.scss",
      "import/layouts/common/_header.sass"
   ],
   "names":[],
   "mappings":"AAAA,4ECQA,KACE,uBACA,0BACA,6BAA8B,CAOhC,KACE,QAAS,CAaX,2FAaE,aAAc,CAQhB,4BAIE,qBACA,uBAAwB,CAQ1B,sBACE,aACA,QAAS,CAQX,kBAEE,YAAa,CAUf,EACE,4BAA6B,CAQ/B,iBAEE,SAAU,CAUZ,YACE,wBAAyB,CAO3B,SAEE,gBAAiB,CAOnB,IACE,iBAAkB,CAQpB,GACE,cACA,eAAgB,CAOlB,KACE,gBACA,UAAW,CAOb,MACE,aAAc,CAOhB,QAEE,cACA,cACA,kBACA,uBAAwB,CAG1B,IACE,UAAW,CAGb,IACE,cAAe,CAUjB,IACE,QAAS,CAOX,eACE,eAAgB,CAUlB,OACE,eAAgB,CAOlB,GACE,uBACA,QAAS,CAOX,IACE,aAAc,CAOhB,kBAIE,iCACA,aAAc,CAkBhB,sCAKE,cACA,aACA,QAAS,CAOX,OACE,gBAAiB,CAUnB,cAEE,mBAAoB,CAWtB,0EAIE,0BACA,cAAe,CAOjB,sCAEE,cAAe,CAOjB,iDAEE,SACA,SAAU,CAQZ,MACE,kBAAmB,CAWrB,2CAEE,sBACA,SAAU,CASZ,gGAEE,WAAY,CAQd,qBACE,6BACA,sBAAuB,CASzB,mGAEE,uBAAwB,CAO1B,SACE,yBACA,aACA,6BAA8B,CAQhC,OACE,SACA,SAAU,CAOZ,SACE,aAAc,CAQhB,SACE,gBAAiB,CAUnB,MACE,yBACA,gBAAiB,CAGnB,MAEE,SAAU,CCnaV,KACE,qBAAsB,CAItB,qBAGE,kBAAmB,CCXzB,EACC,SAAU,CAAA",
   "file":"main.css",
   "sourceRoot":"../../sass/"
}

Any help would be appreciated. Thanks