webpack: Non-deterministic output breaking long-term caching

While using webpack for a project using react-bootstrap, I noticed my distribution hashes kept changing. I’ve narrowed this down to a simple test case, in my situation both react-bootstrap and react-bootstrap-daterangepicker are affected. This is mainly an issue for long-term caching as the hashes for files keep changing.

What happens is that whenever I execute webpack, the output will be different. Looking at diffs between runs it seems that the indexes passed into requires keep changing. Probably some async operations returning in variable order somewhere? Example diff chunk:

141c141
<       !(__WEBPACK_AMD_DEFINE_ARRAY__ = [__webpack_require__(5), __webpack_require__(4), exports], __WEBPACK_AMD_DEFINE_RESULT__ = function(momentjs, $, exports) {

---
>       !(__WEBPACK_AMD_DEFINE_ARRAY__ = [__webpack_require__(6), __webpack_require__(4), exports], __WEBPACK_AMD_DEFINE_RESULT__ = function(momentjs, $, exports) {

Repro case exists out of a package.json to install the requirements and a webpack config:

package.json:

{
    "name": "webpack-repro",
    "version": "0.0.0",
    "dependencies": {
        "react-bootstrap": "0.20.1",
        "react-bootstrap-daterangepicker": "0.2.4"
    },
    "devDependencies": {
        "webpack": "1.7.3"
    },
    "private": true
}

webpack.config.js:

'use strict';

var path = require("path");
var webpack = require("webpack");

module.exports = {
  entry: {
    vendor: [
      "react-bootstrap",
      // "react-bootstrap-daterangepicker",
    ],
  },
  output: {
    path: path.join(__dirname, "js"),
    filename: "[name].js",
  }
};