My point of view is as follows:
The original translation feels like an HTML *field* should be ... a *date*. In Russian language it sounds wierd and it is more natural when you say "A field should *contain* a date" instead of "A field should *be* a date". Don't you agree?

"Поле Date должно быть датой после 9 апреля" vs "В поле Date должна быть дата после 9 апреля".