The function html_calendar in roundup/cgi/templating.py produces a help link that pops up a calendar for date selection.

This computes navigation links in the calendar:

date_prev_month = display + date.Interval("-1m")
date_next_month = display + date.Interval("+1m")

This fails on day 31 of a month due to limitations in our Date/Interval classes:

>>> from roundup import date
>>> d = date.Date ('2022-05-31')
>>> d + date.Interval ('+1m')
<Date 2022-07-01.00:00:00.000>
>>> d + date.Interval ('-1m')
<Date 2022-05-01.00:00:00.000>


Maybe that should be fixed by explicitly incrementing only the month of the given date.
On the other hand it only happens every two months :-)