Lunar months, and why they don't sync with the year

Scarterra has a 365 day year. The passage of time is marked by two concurrent calendars.
The five days at the end of the year mark the anniversary of the the Divine Rebellion and what would otherwise be perfect symmetry of twelve thirty-day months or nine forty-day months.
One wonders why lunar months skew this pattern with a twenty-eight day lunar cycle.
Why is this one of the few places that doesn't match the number nine based numerology of the universe?
The leading theory is that there is a 28-day lunar cycle rather than a 27-day or 36-day lunar cycle Zarthus is a bit of a rascal. He set the lunar cycle just a little bit off of the number nine as a sort of snub to his more hidebound divine siblings: Khemra, Hallisan, and Phidas.

Manifestation

The moon goes through a full cycle every twelve days. Each "quarter" of the moon lasts an even seven days. As a result, most locations recognize some form of a seven-day week rather than a nine-day week though relatively few places agree on what to name the seven days of the week.