This is in 8.1.4. I don’t see anything in the 8.1.5 changelogs, so I’d guess it applies in the nightly as well.
It looks like it’s grabbing the ending day numbers from the month before last, rather than the last month. In March we see January’s ending day number (grey 31 at start):
In April we get the ending numbers from February (grey 25-28):