invalidly formatted dates in listObjects fromDate / toDate parameters do not result in InvalidRequest
instead, the filters are not applied, and unfiltered results are returned.
The call should return an InvalidRequest error with explanation.
This is especially devious when someone doesn't escape the '+' in the timezone field, and it gets decoded to space, resulting in an invalid date format, and incorrect filtering.
Checking the svn logs on CNResourceHandler, (added in r6622) there isn't a specific reason it was put in, so it should be safe to change.