doc.save() throw duplicate error after insertMany, if doc is from error.insertedDocs in ordered:false insertMany

[fabiel-leon]

doc.save() throw duplicate error after insertMany error insertMany(items,{ordered:false}) if doc is from error.insertedDocs

MongoError: E11000 duplicate key error collection: sharednews.news index: id dup key: { : ObjectId('5fcf184a7ad701402cdb49c7') }
at Function.create (/node_modules/mongodb/lib/core/error.js:57:12)
at toError (/node_modules/mongodb/lib/utils.js:123:22)
at /node_modules/mongodb/lib/operations/common_functions.js:265:39
at handler (/node_modules/mongodb/lib/core/sdam/topology.js:942:24)
at /node_modules/mongodb/lib/cmap/connection_pool.js:350:13
at handleOperationResult (/node_modules/mongodb/lib/core/sdam/server.js:558:5)
at MessageStream.messageHandler (/node_modules/mongodb/lib/cmap/connection.js:277:5)
at MessageStream.emit (events.js:310:20)
at processIncomingData (/node_modules/mongodb/lib/cmap/message_stream.js:144:12)
at MessageStream._write (/node_modules/mongodb/lib/cmap/message_stream.js:42:5)
at doWrite (_stream_writable.js:403:12)
at writeOrBuffer (_stream_writable.js:387:5)
at MessageStream.Writable.write (_stream_writable.js:318:11)
at Socket.ondata (_stream_readable.js:695:22)
at Socket.emit (events.js:310:20)
at addChunk (_stream_readable.js:286:12) {
driver: true,
index: 0,
code: 11000
}

class News {
  // findByFullName() becomes a static
  static async shortMany(items) {
    let inserted = [];
    try {
      const insertResult = await this.insertMany(items, { ordered: false });
      inserted = insertResult; // works fine
    } catch ({ insertedDocs }) {
      console.log('inserting error');
      if (insertedDocs) {
        inserted = insertedDocs;  // in this docs .save() throw duplicate error
      }
    }
    console.log(inserted.lenght);
    const results = await async.eachSeries(inserted, async (item) => {
      try {
        const data = await bitly.shorten(item.link);
        item.short = data.link;
        return item.save();  // throw error if doc is from error.insertedDocs after insertMany
      } catch (error) {
        console.error('shorting', error);
      }
    });

    return inserted;
  }
}

ItemSchema.loadClass(News);

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If the current behavior is a bug, please provide the steps to reproduce.

What is the expected behavior?

What are the versions of Node.js, Mongoose and MongoDB you are using? Note that "latest" is not a version.