Steps to reproduce

1.  Open stories app and edit one of the existing stories
2.  Add a new block with a date field between two existing blocks
3. Without filling the date field click on save

Expected results

As Date field is mandatory, the corresponding validation message appears

Actual results

No validation message appears and the form is not saved. If the field is not shown on the current screen as the story is long enough (because you have scrolled up/down to fill other fields), it leads to confusion without the error prompting 

Workaround

The date field remains in red color so it can be found and fixed