When clicking on a date field input box, the calendar appears to choose your date.
You can click on a day to select that date or manually input the date using the keyboard.
Actually to dismiss the date choosing dialog you have to left click somewhere outside the dialog or press the ESC key on the keyboard. This is slightly counterintuitive since the ESCape key is often (always?) associated to an “abort command” behaviour.
While the ESC keypress on the input date can be left as is, I think that the ENTER (RETURN) key should be added to implement a “Confirm my input and go on” behaviour fot those using keyboard to input commands. When the ENTER key is pressed the choose date dialog should be closed and the input should be confirmed.