title: Gulp SASS, autoprefixer, minify and sourcemaps generate huge file
body: <p>I'm experiencing strange behaviour using this Gulp configuration to minify my SASS files generating sourcemaps.</p>
  
  <pre><code>'use strict';
  
  var PATH = {
      SRC_DIR: 'src/',
      SRC: {
          IMG: 'img/',
          INDEX: 'index.html',
          JS: {
              DIR: 'js/',
              FILE: [
                  'app.js',
                  '**/*.js',
                  'controller/**/*.js',
                  'factory/**/*.js',
                  'directive/**/*.js',
                  'model/**/*.js'
              ]
          },
          SASS: 'sass/',
          TEMPLATE: 'template/'
      },
      DEST_DIR: 'dist/',
      DEST: {
          CSS: {
              DIR: 'css/',
              FILE: 'full.css'
          },
          IMG: 'img/',
          JS: {
              DIR: 'js/',
              FILE: 'full.js'
          },
          LIB: 'lib/',
          TEMPLATE: 'template/',
      }
  };
  
  var gulp = require('gulp'),
      autoprefixer = require('gulp-autoprefixer'),
      concat = require('gulp-concat'),
      minifyCss = require('gulp-minify-css'),
      rename = require('gulp-rename'),
      sass = require('gulp-ruby-sass'),
      sourcemaps = require('gulp-sourcemaps');
  
  gulp.task('styles', function() {
      return sass(PATH.SRC_DIR + PATH.SRC.SASS, {
          sourcemap: true,
          style: 'expanded'
      })
      .pipe(autoprefixer({
          browsers: ['last 2 version', 'safari 5', 'ie 8', 'ie 9'],
          cascade: true
      }))
      .pipe(concat(PATH.DEST.CSS.FILE))
      .pipe(gulp.dest(PATH.DEST_DIR + PATH.DEST.CSS.DIR))
      .pipe(rename({suffix: '.min'}))
      .pipe(minifyCss())
      .pipe(sourcemaps.write())
      .pipe(gulp.dest(PATH.DEST_DIR + PATH.DEST.CSS.DIR));
  });
  
  gulp.task('watch', function() {
      gulp.watch(PATH.SRC_DIR + PATH.SRC.SASS + '**/*.scss', ['styles']);
  });
  
  gulp.task('default', ['watch', 'styles']);
  </code></pre>
  
  <p>The first time I run this script using <code>gulp</code> it'll generate a correct <code>full.min.css</code> and it waits for changes in the SASS directory.</p>
  
  <p>When you change something inside SASS files it'll trigger the watch and re-run the <code>styles</code> task, which will build a <code>full.min.css</code>.</p>
  
  <p>You see the changes in the front-end but this minified file becomes bigger and bigger at every rebuild.</p>
  
  <p>If I omit the sourcemaps inside <code>styles</code> task it seems to work fine.
  The <code>full.css</code> file is always ok.</p>
  
  <p>What am I missing here? Why the minified version keeps increasing its dimension?</p>