Seems like a bug because this was already addressed here:
“The behavior when adding a month or changing the month such that the new month is shorter than the old one is different. Previously, adding one month to Jan 31, 2018 would give Mar 3, 2018, because Feb is three days shorter than Jan. Now, adding one month to Jan 31 gives Feb 28: instead of rolling the extra days over, we clamp them down to the last day of the month. We think this behavior better captures what people intuitively expect when they add “one month”.”