Problem with includeAllSources, webpack and isparta-instrumenter

Using the `isparta-instrumenter` with `webpack` and `karma-coverage` I can't make the option `includeAllSources` to work.

Here is my webpack config:

``` javascript
{
/** ... */,
module: {
preLoaders: [
{
test: /\.jsx?$/,
include: path.resolve('src'),
loader: 'isparta-instrumenter'
}
],
loaders: /** ... */
},
/** ... */
}
```

Here is the `karma.conf.js`:

``` javascript
config.set({
basePath: path.resolve('.'),
frameworks: ['mocha'],
files: [
'tests/EntryPoint.js'
],
preprocessors: {
'tests/**/*.js': ['webpack']
},
webpack: webpackConfig,
webpackMiddleware: {
stats: statsOptions
},
reporters: ['progress', 'coverage'],
coverageReporter: {
type: 'html',
dir: 'coverage',
includeAllSources: true
},
port: 9876,
colors: true,
logLevel: config.LOG_INFO,
autoWatch: true,
browsers: ['Chrome'],
captureTimeout: 60000,
singleRun: true,
plugins: [
'karma-webpack',
'karma-mocha',
'karma-coverage',
'karma-chrome-launcher'
]
});
```

I get the html output but the untested files are missing. Did anybody make this option work with `isparta-instrumenter` and `webpack`? I'm pretty sure there is no issue here but I can't find the correct configuration.

I tried adding `coverage` as a preprocessor for my source file but it seems to fail because they are ES6 or JSX files.