Promise.all get stuck with mongodb

I have this code where I only get result from 1 Promise, I tried each one individually by commenting one of them, they actually resolve with no error, but when they are together, i only get the result of the first one. But not from Promise.all, only the console.log inside the Promise gets called

var mongodb = require('mongodb');
var Promise = require('bluebird');

var $ = mongodb.MongoClient.connect('mongodb://nobody:nobody@localhost/dbauth');
$.then(
(db) => {
    var p1 = new Promise(
     (resolve, reject) => {
        var dbx = db.db('db1');
        dbx.authenticate('user1', 'user1').then((x) => {
            console.log(x); // true
            var o = dbx.stats();
            o.then(
               (result) => {
                  console.log(result);
                  resolve(result);
               }
            ).catch(
               (err) => {
                   reject(err);
               }
            );
        });
     });

    var p2 = new Promise(
     (resolve, reject) => {
       var dbx = db.db('db2');
       dbx.authenticate('user2', 'user2').then((x) => {
            console.log(x);
            var o = dbx.stats();
            o.then(
               (result) => {
                  console.log(result);
                  resolve(result);
               }
            ).catch(
               (err) => {
                   reject(err);
               }
            );
       });
    });

    return Promise.all([p1,p2]).then(
        (res) => {
            res.forEach(console.log);
        }
    ).catch(console.log);
}).catch(console.log);

what prints is this

true // from console.log(x); of p1
true // from console.log(x); of p2
{ db: 'db1',
  collections: 2,
  views: 0,
  objects: 0,
  avgObjSize: 0,
  dataSize: 0,
  storageSize: 8192,
  numExtents: 0,
  indexes: 2,
  indexSize: 8192,
  ok: 1 } // from console.log(res) of p1

but the same code will work fine if I remove this part from the code from both promises and call resolve(x) instead

                o.then(
                   (result) => {
                      console.log(result);
                      resolve(result);
                   }
                ).catch(
                   (err) => {
                       reject(err);
                   }
                );

Promise.all([p1]);

why actually the promise is being executed before it comes to Promise.all ?

via user7887107