Suppose you have a Date input field, and someone first enters a date in
that field in a format not recognized by Roundup, then uses the calendar
widget (_generic.calendar.html) to edit the date.

This uses html_calendar, which does

    curr_date = date.Date(date_str) # to highlight

which produces a Templating Error email to the admin with a backtrace
when it cannot parse the date.

Whatever is done with a badly formatted date - a message to the user
about valid date formats would seem sensible - giving a Templating Error
like that isn't user-friendly or the right thing to do.

Thanks for reporting that Joseph.

I had a little difficulty reproducing it. I was only able to
do it if I submitted an invalid date and got an error.

Once I did that the bad date was passed to the calendar popup.

I have changed to code to catch the error and highlight today's date in
the calendar.

I will open a new issue/feature request to enhance the calendar
popup and javascript code to use the current value in the date
field rather than the last submitted value.