In message
<1488196866.65.0.830643908552.issue2550935@psf.upfronthosting.co.za> ,
Thomas Arendsen Hein writes:

>I have seen this, too.
>It does not need submit, it happens while editing an issue.
>
[elided correct direcions to reproduce]
>When fixing this: Beware about invalid dates, as there was no error
>checking at this point.

The lack of error handling was the cause of issue2550932.

The fix was to catch the exception if the date passed to roundup to
display the calendar was invalid. This stops the traceback. In that
case the calendar highlights today.

Since using the current date selector requires javascript, I have been
wondering if a pure javascript date selector may be useful. It should
be faster. Also many browsers have built in date selectors if the
input type is set properly (maybe to date??).

I am not sure if we should go one of those routes. In the input
type=date case, it will fall back to a text input box. Without
javascript enabled the (cal) link should not be displayed (but it is
which seems to be a bug in our classic ... templates).