add().days().toString() returns different dates depending on format chosen

```
What steps will reproduce the problem?

new Date('Nov 14, 2014').add(3).days().toString('MMM d, yyyy') returns Nov
17,2014

new Date('2014-11-14').add(3).days().toString('yyyy-MM-dd') returns 2014-11-16

What is the expected output? What do you see instead?
I expected them to return the same date

What version of the product are you using? On what operating system?
Version: 1.0 Alpha-1 on linux server
browser tested: Firefox Mac

Please provide any additional information below.

```

Original issue reported on code.google.com by `r...@ethos7.com` on 26 Jan 2014 at 8:12