There is a similar problem with the 20th sun of the Fifth Asttral Moon (e.g. 9/20) reporting itself as 9/19--this issue has been in since 1.x and they have repeatedly not fixed it. I even think they acknowledged it at one point in beta, but never addressed it.

The issue in the Fifth Astral moon (e.g. 9th month) was that two days earlier in the month had the same numeric representation, e.g. 6th sun reported 9/6, and the 7th sun reported 9/6 as well. (Don't remember the exact days that duplicated their date format)