I'm not sure I fully understood what you did and what you expected. When you change a calendar on the edit page, the years also need to be changed, as they will be expected to be based on the calendar you selected.
When changing the calendar instead of having 1800 = 5 it stay1800 of republican calendar. Now with all correction made I can't reproduce this error. You can set up this ticket as rejected.
Always look on the bright side of life!
Status changed to Rejected(Xavier, 25 Sep 2023, 21:52)