When you check if two dates are equal to each other you run the following code:

if ((0, _utils.isDate)(l) || (0, _utils.isDate)(r)) {
if (l.toString() == r.toString()) return {};
return r;
}
The issue here is that new Date(1).toString() === new Date(2).toString() //true which is obviously false.

The issue here is that toString formats the date object into a human readable format which does not take milliseconds into account Mon Sep 28 1998 14:36:22 GMT-0700 (PDT)

What you should be using instead is .valueOf() which converts the date into an epoch time. This is also much more preferment than toStirng: roughly 25x faster in node 7.