Why CommonChunksPlugins does not remove Commons Chunk Code

Do you want to request a feature or report a bug?

What is the current behavior?
RT
If the current behavior is a bug, please provide the steps to reproduce.
I have a multi Page app and I have two enties ‘main.js’,’main2.js’ for two pages.

//main.js
require(['./a','./b','./c'],function(){
    console.log('main')
})

//main2.js
require(['./a','./b','./d'],function(){
    console.log('main')
})

as you see. two entries share common ‘./a’, ‘,/b’.
if bundle the code now , ‘./a’, ‘,/b’ will apear twice , result in large file size if they are big files
then I want to use CommonsChunksPlugins to remove duplicate module like

//webpack.config.js
new webpack.optimize.CommonsChunkPlugin({
	async: true,
        minChunks: 2
})

nothing change… then i change to

    entry:{
        main:'./main.js',
        main2:'./main2.js',
        common:['./a','./b']
    },
    plugins: [
	 new webpack.optimize.CommonsChunkPlugin({
		name: ['share','common'],
		async: true,
               minChunks: 2
	  })
	]

this time it generate share.js contain ‘./a’, ‘,/b’.
but entries main.js and main2.js still contain ‘./a’, ‘,/b’. it does not reduce ouptsize

What is the expected behavior?
extract common modules from entries to #share.js
Please mention other relevant information such as the browser version, Node.js version, webpack version and Operating System.
Window10
Webpack 2.2.0
node 6.9.2