Inconsistent behavior of .diff() with "month" unit

```
console.log(dayjs("2020-02-14").diff(dayjs("2020-02-01"), "month", true));
console.log(dayjs("2020-03-01").diff(dayjs("2020-02-14"), "month", true));
console.log(dayjs("2020-02-14").diff(dayjs("2020-02-01"), "month", true) + dayjs("2020-03-01").diff(dayjs("2020-02-14"), "month", true));
console.log(dayjs("2020-03-01").diff(dayjs("2020-02-01"), "month", true));
```

The result is the following:
```
0.41935483870967744
0.5517241379310345
0.971078976640712
1
```

I have tried with different time units, including adding time and timezone, but no change in the behavior. Other months produce different results, looks like only January and July has it correct.

Chrome 78, Windows 10 if it matters.