When the calendar loads in a month that is short, say February, the endsAt is set as the 28th (unless it's a leap year)
When you hit goToPreviousMonth to go to January, the package is doing $this->endsAt->subMonthNoOverflow() which is keeping the end date for January as 28th
goToPreviousMonth
to go to January, the package is doing $this->endsAt->subMonthNoOverflow() which is keeping the end date for January as 28thAdded tests to illustrate the scenario.