"moment().add(1,'d')" doesn't behave as expected around timezone changes

[jodevsa]

Hi there,

After reviewing an issue in Cron; a library that utilizes moment-timezone for time zone support. We were able to trace it back to the unexpected behavior occurring from reading date.days() value after triggering date.add(1,'d')`

Steps to reproduce:

const moment = require('moment-timezone');
const date= moment.tz(new Date("Sat Nov 03 2018 00:00:00 GMT-0300"),"America/Sao_Paulo")
console.log(date.days());
console.log(date.toString()); // outputs: Sat Nov 03 2018 00:00:00 GMT-0300
date.add(1,'d');
console.log(date.days())
console.log(date.toString())  // outputs: Sat Nov 03 2018 23:00:00 GMT-0300 but should be  Sat Nov 04 2018 00:00:00 GMT-0200

[jodevsa]

I understand that this might be due to timezone changes but even date.day() remain unchanged after the add

[mattjohnsonpint]

Duplicate of #409. Tracking there. Thanks.