When clicking on a day in the calendar, it always shows the moon phases for the 1st month although it states the correct month in the popup. Below shows the popup for the 15th day of the first month, the second screenshot shows the 15th day of the second month.

Correct for first month.

Popup shows the same (incorrect) phases for the 2nd month. It always shows the phases for the first month in the popup.

I tried it on my Mac in Safari as well - same issue.

Click on a day on any month other than the first month and the popup shows the first month's celestial phases instead of the month desired.