When choosing, what I guess is supposed to be your character's birth day, the selection options seem to be bugged. As I hover over dates, I notice the numerical date (X/Y) does not match with the text date (X Sun of the Y Astral Moon). As you hover your mouse over the dates, you'll eventually see discrepancies between the two. It seems to be different for each month you go through. I should note this is for the PC version.