Should not be able to create an event without giving a date

Currently it is possible to create a new event without explicitly giving a date; the event is then created with the current date and time as start date and an end date as start date + 30minutes.

This can happen quite easily if one clicks on the "Create new event" button instead into the calendar widget (in the latter case the date is prefilled). If one types in a title and then uses "Enter" instead of "Tab", the new event is created without error message.