title: webpack-dev-server doesn't watch/recompile files if they import named exports
body: <h2>Problem</h2>
  <p>This is the craziest webpack issue I ever saw. You don't want to know the amount of time debugging took to find the problem. I have a pretty basic <code>webpack.config.js</code>:</p>
  <pre><code>const path = require('path');
  const webpack = require('webpack');
  
  module.exports = {
      entry: path.resolve(__dirname, 'app/index.js'),
      output: {
          path: path.join(__dirname, 'build'),
          filename: 'boundle.js',
      },
      module: {
          rules: [
              {
                  test: /\.jsx?$/,
                  use: [
                      'babel-loader',
                  ],
                  exclude: /node_modules/
              },
          ],
      },
      plugins: [
          new webpack.HotModuleReplacementPlugin(),
      ],
  };
  </code></pre>
  <p>Then I import a few files in <code>app/index.js</code>:</p>
  <pre><code>import React from 'react';
  import ReactDOM from 'react-dom';
  import { Provider } from 'react-redux';
  import { createStore, applyMiddleware } from 'redux';
  import thunk from 'redux-thunk';
  import ControlPanel from './scenes/ControlPanel/index.js';
  // This last file can be empty. Just import a custom file.
  </code></pre>
  <p>If I run <code>./node_modules/.bin/webpack-dev-server</code> everything compiles and works fine, but if I modify/save <code>app/scenes/ControlPanel/index.js</code> webpack-dev-server doesn't update. If I save <code>app/index.js</code> it recompile properly but it doesn't do anything for the other file.</p>
  <p>I have:</p>
  <ul>
  <li>Ubuntu 16.04</li>
  <li>Node.js 4.2.6</li>
  <li>webpack-dev-server 2.4.1</li>
  </ul>
  <h2>The cause</h2>
  <p>Lets remove the imports below (the only ones that import named exports, aka use the <code>import { ... }</code> syntax).</p>
  <pre><code>import { Provider } from 'react-redux';
  import { createStore, applyMiddleware } from 'redux';
  </code></pre>
  <p>Now everything works fine again. If I save <code>app/scenes/ControlPanel/index.js</code> it recompile successfully. What? Why? Why was it able to compile only for the first time when I start webpack-dev-server? Why webpack-dev-server has a problem with this syntax?</p>
  <h2>Workaround (where real madness starts)</h2>
  <p>I found a workaround that (at least) makes development possible. You aren't gonna believe it: If I delete the whole content of <code>app/index.js</code>, hit save a couple of times, then undo the deletion to get back to the original state and hit save a couple of times again, then I go to save <code>app/scenes/ControlPanel/index.js</code>, it works again. Usually... Of course if that file imports named exports too then it won't work.</p>
  <p>What is even more crazy is that if I import named exports from one of my custom files, it works, so it only hates imports from <code>node_modules</code>.</p>
  <h2>The End</h2>
  <p>The cherry on top is that I waited a day to post this question. Today I turned on my PC and nothing works. It doesn't detect any changes. I haven't modified a single character since the last time it worked.</p>