Incredible annoying behavior with GRUNT

We're using Mean.io for a project and getting erratic behavior from Grunt.

When we make changes on different files (while Grunt is running, of course), Grunt may detect the changes or not. HTML changes are usually detected by Grunt, but CSS/JS changes not.

And even worst, we often have to reboot (CTRL+C, grunt -f) Grunt to make it displays the project correctly because it prints random errors that actually don't exist. And thus the page is not displayed correctly in the browser.

For instance:

/vagrant/vavel/node_modules/dependable/index.js:115
        throw new Error("dependency '" + name + "' was not registered");
          ^
Error: dependency 'access' was not registered

Or:

/vagrant/vavel/node_modules/mongoose/lib/index.js:323
      throw new mongoose.Error.MissingSchemaError(name);
        ^
MissingSchemaError: Schema hasn't been registered for model "User".
Use mongoose.model(name, schema)

These errors just disappear if we restart Grunt again (using "rs" or CTRL+C + grunt -f).

In fact, sometimes there is not any error displayed in console and the page doesn't show up well.

Are we doing something wrong with ow we are using Grunt?

Gruntfile.js

cat Gruntfile.js

'use strict';

var paths = {
  js: ['*.js', 'test/**/*.js', '!test/coverage/**', '!bower_components/**', 'packages/**/*.js', '!packages/**/node_modules/**'],
  html: ['packages/**/public/**/views/**', 'packages/**/server/views/**'],
  css: ['!bower_components/**', 'packages/**/public/**/css/*.css']
};

module.exports = function(grunt) {

  if (process.env.NODE_ENV !== 'production') {
    require('time-grunt')(grunt);
  }

  // Project Configuration
  grunt.initConfig({
    pkg: grunt.file.readJSON('package.json'),
    assets: grunt.file.readJSON('config/assets.json'),
    clean: ['bower_components/build'],
    watch: {
      js: {
        files: paths.js,
        tasks: ['jshint'],
        options: {
          livereload: true
        }
      },
      html: {
        files: paths.html,
        options: {
          livereload: true,
          interval: 500
        }
      },
      css: {
        files: paths.css,
        tasks: ['csslint'],
        options: {
          livereload: true
        }
      }
    },
    jshint: {
      all: {
        src: paths.js,
        options: {
          jshintrc: true
        }
      }
    },
    uglify: {
      core: {
        options: {
          mangle: false
        },
        files: '<%= assets.core.js %>'
      }
    },
    csslint: {
      options: {
        csslintrc: '.csslintrc'
      },
      src: paths.css
    },
    cssmin: {
      core: {
        files: '<%= assets.core.css %>'
      }
    },
    nodemon: {
      dev: {
        script: 'server.js',
        options: {
          args: [],
          ignore: ['node_modules/**'],
          ext: 'js,html',
          nodeArgs: ['--debug'],
          delayTime: 1,
          cwd: __dirname
        }
      }
    },
    concurrent: {
      tasks: ['nodemon', 'watch'],
      options: {
        logConcurrentOutput: true
      }
    },
    mochaTest: {
      options: {
        reporter: 'spec',
        require: [
          'server.js',
          function() {
            require('meanio/lib/util').preload(__dirname + '/packages/**/server', 'model');
          }
        ]
      },
      src: ['packages/**/server/tests/**/*.js']
    },
    env: {
      test: {
        NODE_ENV: 'test'
      }
    },
    karma: {
      unit: {
        configFile: 'karma.conf.js'
      }
    }
  });

  //Load NPM tasks
  require('load-grunt-tasks')(grunt);

  //Default task(s).
  if (process.env.NODE_ENV === 'production') {
    grunt.registerTask('default', ['clean', 'cssmin', 'uglify', 'concurrent']);
  } else {
    grunt.registerTask('default', ['clean', 'jshint', 'csslint', 'concurrent']);
  }

  //Test task.
  grunt.registerTask('test', ['env:test', 'mochaTest', 'karma:unit']);

  // For Heroku users only.
  // Docs: https://github.com/linnovate/mean/wiki/Deploying-on-Heroku
  grunt.registerTask('heroku:production', ['cssmin', 'uglify']);
};