Random fail with large amount of PHP files

[Sweetchuck]

For testing purposes a I tried to lint the /core directory of Drupal 8. It contains ~6200 PHP files.

It takes ~17sec to run this command:
time find ./ -type f \( -name '*.php' -or -name '*.inc' -or -name '*.install' -or -name '*.profile' \) -print0 | xargs -0 -P8 -n1 php -n -d sort_open_tag=Off -d asp_tags=Off -l

real    0m16.946s
user    1m10.360s
sys     0m24.196s

I am using the following configuration to achieve the same thing with grunt-phplint

grunt.initConfig({
    phplint: {
        core: {
            options: {
                cache: false,
                spawnLimit: 8,
                phpArgs: {
                    '-n': null,
                    '-d': [
                        'sort_open_tag=Off',
                        'asp_tags=Off'
                    ]
                }
            },
            files: [
                {
                    src:['core/**/*.{php,inc,module,install,profile}']
                }
            ]
        }
    }
});

The problem is that it randomly fails, but every time at a different PHP file.
The error message is:

Fatal error: Cannot read property 'on' of undefined
TypeError: Cannot read property 'on' of undefined
    at Object.PhpLintCommandWrapper.lintFile (/.../grunt-phplint/tasks/core/PhpLintCommandWrapper.js:24:20)
    at /.../grunt-phplint/tasks/core/PhpLintTask.js:73:11
    at Object.PhpLintTask._checkCached (/.../grunt-phplint/tasks/core/PhpLintTask.js:116:11)
    at Object.PhpLintTask._lintFile (/.../grunt-phplint/tasks/core/PhpLintTask.js:60:8)
    at bound (/.../grunt-phplint/node_modules/grunt-legacy-util/node_modules/lodash/lodash.js:573:19)
    at replenish (/.../grunt-phplint/node_modules/grunt-legacy-util/node_modules/async/lib/async.js:144:17)
    at /.../grunt-phplint/node_modules/grunt-legacy-util/node_modules/async/lib/async.js:156:29
    at /.../grunt-phplint/tasks/core/PhpLintTask.js:95:13
    at ChildProcess.<anonymous> (/.../grunt-phplint/tasks/core/PhpLintCommandWrapper.js:37:4)
    at emitTwo (events.js:87:13)

When I decrease the options.spawnLimit to 4 or less it works as expected.

I have added a console.log() to see what is there.

PhpLintCommandWrapper.prototype = {

    lintFile: function(filePath, done) {
        var cmdArgs = this._parseOptions(this.options.phpArgs),
            phpLintCmd = spawn(this.options.phpCmd, cmdArgs.concat([filePath])),
            output = "";

        if (typeof phpLintCmd.stdout === 'undefined') {
            console.log(JSON.stringify(Object.keys(phpLintCmd), null, 2));
        }

                // Line 24.
        phpLintCmd.stdout.on("data", function(data) {
            output += data;
        });
                // ...
    }
}

Running "phplint:core" (phplint) task
[D] Task source: tasks/phplint.js
[
  "domain",
  "_events",
  "_eventsCount",
  "_maxListeners",
  "_closesNeeded",
  "_closesGot",
  "connected",
  "signalCode",
  "exitCode",
  "killed",
  "spawnfile",
  "_handle",
  "spawnargs"
]
Fatal error: Cannot read property 'on' of undefined
TypeError: Cannot read property 'on' of undefined
    at Object.PhpLintCommandWrapper.lintFile (/.../grunt-phplint/tasks/core/PhpLintCommandWrapper.js:24:20)