Why does foo, bar, and baz depend on all three vendor bundles?

bar.js

const moment = require("moment");
module.exports = "bar";

baz.js

const immutable = require("immutable");
module.exports = "foo";

foo.js

const icepick = require("icepick");
module.exports = "foo";

my-plugin.js

function MyPlugin(options) {
    // Configure your plugin with options...
}

const getAllDeps = (chunk) => {
    if (chunk.parents.length > 0) {
        const result = [];
        for (const parent of chunk.parents) {
            result.push(...getAllDeps(parent));
        }
        result.push(...chunk.parents.map(parent => parent.id));
        return result;
    } else {
        return [];
    }
};

MyPlugin.prototype.apply = function(compiler) {
    compiler.plugin("compilation", function(compilation) {
        compilation.plugin("record-chunks", function(chunks, records) {
            console.log('chunk: [depdencies]');
            console.log('-------------------');

            const lookup = {};
            for (const chunk of chunks) {
                lookup[chunk.id] = chunk.name;
            }

            for (const chunk of chunks) {
                console.log(`${lookup[chunk.id]}: [${getAllDeps(chunk).map(chunkId => lookup[chunkId])}]`);
            }
            console.log('');
        });
    });
};

module.exports = MyPlugin;

output

chunk: [depdencies]
-------------------
vendor2: [vendor3]
vendor1: [vendor3,vendor2]
foo: [vendor3,vendor2,vendor1]
baz: [vendor3,vendor2,vendor1]  // require immutable, I would expend it to depend on vendor3 only
bar: [vendor3,vendor2,vendor1]
vendor3: []

Hash: 4a75e5ed5b4081369fc7
Version: webpack 3.8.1
Time: 632ms
           Asset       Size  Chunks                    Chunk Names
vendor2.entry.js     479 kB       0  [emitted]  [big]  vendor2  // contains moment
vendor1.entry.js    14.2 kB       1  [emitted]         vendor1  // contains icepick
    foo.entry.js  173 bytes       2  [emitted]         foo
    baz.entry.js  177 bytes       3  [emitted]         baz
    bar.entry.js  172 bytes       4  [emitted]         bar
vendor3.entry.js     148 kB       5  [emitted]         vendor3  // contains immutable and the webpackJsonp implementation

webpack.config.js

const path = require('path');
const webpack = require('webpack');
const MyPlugin = require('./my-plugin.js');

module.exports = {
    entry: {
        'foo': './src/foo.js',
        'bar': './src/bar.js',
        'baz': './src/baz.js',
        'vendor1': ['icepick'],
        'vendor2': ['moment'],
        'vendor3': ['immutable'],
    },
    output: {
        path: path.resolve(__dirname, 'dist'),
        filename: '[name].entry.js',
    },
    plugins: [
        new webpack.optimize.CommonsChunkPlugin({
		names: ["vendor1", "vendor2", "vendor3"],
			minChunks: Infinity
		}),
        new MyPlugin({}),
    ]
};