Webpack import sub module bug

0.js

// ./dist/0.js

webpackJsonp([0],[
/* 0 */,
/* 1 */
/***/ function(module, exports) {

module.exports = function() {
    console.log('in module a');
}

/***/ }
]);

entry.js

// ./src/entry.js

function load(subModule) {
    return System.import('./modules/' + subModule);
}

// works
load('module-a/index.js').then(a => {
    console.log('module-a/index.js');
    a();
});

// throws
load('module-a/').then(a => {
    console.log('module-a/');
    a();
});

// throws
load('module-a').then(a => {
    console.log('module-a');
    a();
});

index.js

// ./src/modules/module-a/index.js

module.exports = function() {
    console.log('in module a');
}

main.js

// ./dist/main.js

/******/ (function(modules) { // webpackBootstrap
/******/ 	// install a JSONP callback for chunk loading
/******/ 	var parentJsonpFunction = window["webpackJsonp"];
/******/ 	window["webpackJsonp"] = function webpackJsonpCallback(chunkIds, moreModules, executeModules) {
/******/ 		// add "moreModules" to the modules object,
/******/ 		// then flag all "chunkIds" as loaded and fire callback
/******/ 		var moduleId, chunkId, i = 0, resolves = [], result;
/******/ 		for(;i < chunkIds.length; i++) {
/******/ 			chunkId = chunkIds[i];
/******/ 			if(installedChunks[chunkId])
/******/ 				resolves.push(installedChunks[chunkId][0]);
/******/ 			installedChunks[chunkId] = 0;
/******/ 		}
/******/ 		for(moduleId in moreModules) {
/******/ 			if(Object.prototype.hasOwnProperty.call(moreModules, moduleId)) {
/******/ 				modules[moduleId] = moreModules[moduleId];
/******/ 			}
/******/ 		}
/******/ 		if(parentJsonpFunction) parentJsonpFunction(chunkIds, moreModules, executeModules);
/******/ 		while(resolves.length)
/******/ 			resolves.shift()();

/******/ 	};

/******/ 	// The module cache
/******/ 	var installedModules = {};

/******/ 	// objects to store loaded and loading chunks
/******/ 	var installedChunks = {
/******/ 		1: 0
/******/ 	};

/******/ 	// The require function
/******/ 	function __webpack_require__(moduleId) {

/******/ 		// Check if module is in cache
/******/ 		if(installedModules[moduleId])
/******/ 			return installedModules[moduleId].exports;

/******/ 		// Create a new module (and put it into the cache)
/******/ 		var module = installedModules[moduleId] = {
/******/ 			i: moduleId,
/******/ 			l: false,
/******/ 			exports: {}
/******/ 		};

/******/ 		// Execute the module function
/******/ 		modules[moduleId].call(module.exports, module, module.exports, __webpack_require__);

/******/ 		// Flag the module as loaded
/******/ 		module.l = true;

/******/ 		// Return the exports of the module
/******/ 		return module.exports;
/******/ 	}

/******/ 	// This file contains only the entry chunk.
/******/ 	// The chunk loading function for additional chunks
/******/ 	__webpack_require__.e = function requireEnsure(chunkId) {
/******/ 		if(installedChunks[chunkId] === 0)
/******/ 			return Promise.resolve();

/******/ 		// an Promise means "currently loading".
/******/ 		if(installedChunks[chunkId]) {
/******/ 			return installedChunks[chunkId][2];
/******/ 		}
/******/ 		// start chunk loading
/******/ 		var head = document.getElementsByTagName('head')[0];
/******/ 		var script = document.createElement('script');
/******/ 		script.type = 'text/javascript';
/******/ 		script.charset = 'utf-8';
/******/ 		script.async = true;
/******/ 		script.timeout = 120000;

/******/ 		if (__webpack_require__.nc) {
/******/ 			script.setAttribute("nonce", __webpack_require__.nc);
/******/ 		}
/******/ 		script.src = __webpack_require__.p + "" + chunkId + ".js";
/******/ 		var timeout = setTimeout(onScriptComplete, 120000);
/******/ 		script.onerror = script.onload = onScriptComplete;
/******/ 		function onScriptComplete() {
/******/ 			// avoid mem leaks in IE.
/******/ 			script.onerror = script.onload = null;
/******/ 			clearTimeout(timeout);
/******/ 			var chunk = installedChunks[chunkId];
/******/ 			if(chunk !== 0) {
/******/ 				if(chunk) chunk[1](new Error('Loading chunk ' + chunkId + ' failed.'));
/******/ 				installedChunks[chunkId] = undefined;
/******/ 			}
/******/ 		};

/******/ 		var promise = new Promise(function(resolve, reject) {
/******/ 			installedChunks[chunkId] = [resolve, reject];
/******/ 		});
/******/ 		installedChunks[chunkId][2] = promise;

/******/ 		head.appendChild(script);
/******/ 		return promise;
/******/ 	};

/******/ 	// expose the modules object (__webpack_modules__)
/******/ 	__webpack_require__.m = modules;

/******/ 	// expose the module cache
/******/ 	__webpack_require__.c = installedModules;

/******/ 	// identity function for calling harmony imports with the correct context
/******/ 	__webpack_require__.i = function(value) { return value; };

/******/ 	// define getter function for harmony exports
/******/ 	__webpack_require__.d = function(exports, name, getter) {
/******/ 		if(!__webpack_require__.o(exports, name)) {
/******/ 			Object.defineProperty(exports, name, {
/******/ 				configurable: false,
/******/ 				enumerable: true,
/******/ 				get: getter
/******/ 			});
/******/ 		}
/******/ 	};

/******/ 	// getDefaultExport function for compatibility with non-harmony modules
/******/ 	__webpack_require__.n = function(module) {
/******/ 		var getter = module && module.__esModule ?
/******/ 			function getDefault() { return module['default']; } :
/******/ 			function getModuleExports() { return module; };
/******/ 		__webpack_require__.d(getter, 'a', getter);
/******/ 		return getter;
/******/ 	};

/******/ 	// Object.prototype.hasOwnProperty.call
/******/ 	__webpack_require__.o = function(object, property) { return Object.prototype.hasOwnProperty.call(object, property); };

/******/ 	// __webpack_public_path__
/******/ 	__webpack_require__.p = "";

/******/ 	// on error function for async loading
/******/ 	__webpack_require__.oe = function(err) { console.error(err); throw err; };

/******/ 	// Load entry module and return exports
/******/ 	return __webpack_require__(__webpack_require__.s = 2);
/******/ })
/************************************************************************/
/******/ ([
/* 0 */
/***/ function(module, exports, __webpack_require__) {

var map = {
	"./module-a/index": [
		1,
		0
	],
	"./module-a/index.js": [
		1,
		0
	]
};
function webpackAsyncContext(req) {
	var ids = map[req];	if(!ids)
		return Promise.reject(new Error("Cannot find module '" + req + "'."));
	return __webpack_require__.e(ids[1]).then(function() {
		return __webpack_require__(ids[0]);
	});
};
webpackAsyncContext.keys = function webpackAsyncContextKeys() {
	return Object.keys(map);
};
module.exports = webpackAsyncContext;
webpackAsyncContext.id = 0;


/***/ },
/* 1 */,
/* 2 */
/***/ function(module, exports, __webpack_require__) {

function load(subModule) {
    return __webpack_require__(0)("./" + subModule);
}

// works
load('module-a/index.js').then(a => {
    console.log('module-a/index.js');
    a();
});

// throws
load('module-a/').then(a => {
    console.log('module-a/');
    a();
});

// throws
load('module-a').then(a => {
    console.log('module-a');
    a();
});


/***/ }
/******/ ]);

package.json

{
  "dependencies": {},
  "devDependencies": {
    "html-webpack-plugin": "^2.24.1",
    "webpack": "^2.2.0-rc.3",
    "webpack-dev-server": "^2.2.0-rc.0"
  },
  "scripts": {
    "build": "node_modules/.bin/webpack",
    "serve": "node_modules/.bin/webpack-dev-server"
  }
}

webpack.config.js

const path = require('path');

const webpack = require('webpack');
const HtmlWebpackPlugin = require('html-webpack-plugin');

module.exports = {
  entry: './src/entry.js',
  resolve: {
    modules: [
      path.join(__dirname, 'src'),
      'node_modules'
    ]
  },
  output: {
    path: path.join(__dirname, 'dist'),
    filename: '[name].js'
  },
  plugins: [
    new HtmlWebpackPlugin({
      template: './tmpl/index.ejs'
    })
  ]
};