Counterexample

gistfile1.txt

### package.json
{
  "devDependencies": {
    "grunt": "^0.4.5",
    "grunt-contrib-clean": "^0.6.0",
    "grunt-contrib-less": "^1.0.0",
    "load-grunt-tasks": "^3.1.0"
  }
}

### Gruntfile.js
/*!
 * SIMPLIFIED FORK of Bootstrap's Gruntfile
 * http://getbootstrap.com
 * Copyright 2013-2015 Twitter, Inc.
 * Licensed under MIT (https://github.com/twbs/bootstrap/blob/master/LICENSE)
 */

module.exports = function (grunt) {
  'use strict';

  grunt.initConfig({
    clean: {
      dist: 'dist'
    },

    less: {
      compileCore: {
        options: {
          strictMath: true
        },
        src: 'less/bootstrap.less',
        dest: 'dist/css/bootstrap.css'
      },
      compileTheme: {
        options: {
          strictMath: true
        },
        src: 'less/theme.less',
        dest: 'dist/css/bootstrap-theme.css'
      }
    }

  });

  require('load-grunt-tasks')(grunt, { scope: 'devDependencies' });

  grunt.registerTask('default', ['clean:dist', 'less:compileCore', 'less:compileTheme']);
};

### Setup
1. Copy above files into a new directory (e.g. `foo`)
2. Copy Bootstrap's `less/` directory into the new directory (as e.g. `foo/less/`)
  (Bootstrap version: https://github.com/twbs/bootstrap/commit/984204c39e00d267f49c39d100d0ac2aab8dae9c )
3. npm install
4. grunt
###
Output:

$ grunt
Running "clean:dist" (clean) task
>> 0 paths cleaned.

Running "less:compileCore" (less) task
File dist/css/bootstrap.css created

Running "less:compileTheme" (less) task
File dist/css/bootstrap-theme.css created

Done, without errors.

### Key versions from `npm ls`
├─┬ grunt-contrib-less@1.0.0
[...]
│ ├─┬ less@2.4.0