How to properly configure grunt-contrib-cssmin?

Question

Grunt.js

Hello, there is grunt'a config. (I'm doing it for the first time, don't kick much, what to fix, say, thanks)
They glue the css files, then I minify them. And then the problem crashes, if there are comments in the css file (for example, in animate.css), then after minification the css is all commented out. What am I doing wrong? How is it treated?
Gruntfile.js

module.exports = function (grunt) {

    grunt.initConfig({
        clean: {
            folder: ['build/']
        },
        bower: {
            dev: {
                dest: 'public/',
                js_dest: 'public/js/lib',
                css_dest: 'public/css/lib',
                fonts_dest: 'public/fonts/',
                images_dest: 'public/img/'
            }
        },
        concat: {
            js: {
                src: ['public/js/**'],
                dest: 'public/js/chill.js'
            },
            css: {
                src: ['public/css/**'],
                dest: 'public/css/chill.css'
            }
        },
        autoprefixer: {
            options: {
                browsers: ['last 2 versions', 'ie 8', 'ie 9', '> 1%']
            },
            main: {
                expand: true,
                flatten: true,
                src: 'public/css/chill.css',
                dest: 'public/css/'
            }
        },
        uglify: {
            dist: {
                src: ['<%= concat.js.dest %>'],
                dest: 'build/js/chill.min.js'
            }
        },
        cssmin: {
            dist: {
                src: ['<%= concat.css.dest %>'],
                dest: 'build/css/chill.min.css'
            }
        },
        imagemin: {
            dynamic: {
                files: [{
                    expand: true,
                    cwd: 'public/img',
                    src: ['*'],
                    dest: 'build/img',
                }]
            }
        },
        copy: {
            main: {
                expand: true,
                cwd: 'public/',
                src: ['fonts/*'],
                dest: 'build/'
            }
        },
        clean: {
            css: ['<%= concat.css.dest %>'],
            js: ['<%= concat.js.dest %>']
        }
    });

    grunt.loadNpmTasks('grunt-bower');
    grunt.loadNpmTasks('grunt-contrib-concat');
    grunt.loadNpmTasks('grunt-autoprefixer');
    grunt.loadNpmTasks('grunt-contrib-uglify');
    grunt.loadNpmTasks('grunt-contrib-cssmin');
    grunt.loadNpmTasks('grunt-contrib-imagemin');
    grunt.loadNpmTasks('grunt-contrib-copy');
    grunt.loadNpmTasks('grunt-contrib-clean');

    grunt.registerTask('default', ['bower', 'concat', 'uglify', 'autoprefixer', 'uglify', 'cssmin', 'imagemin', 'copy', 'clean']);
};

Answer 1

Found a solution.
You need to run cssmin with the keepSpecialComments: 0 parameter.
Then all comments are simply deleted, which is actually correct when building the release version.

Answer 2

Everything seems to be correct in the config. Either write a CSS comment in such a clever way that the parser stumbles in cssmin or autoprefixer, or a bug in one of these processors (which is unlikely).