Check that the date that you have entered is a valid date, for example if you try and enter 31 June, 31 November and so on then you will get stuck in that field until you correct the date and make it a valid date.
You can do this by using the backspace key to delete back to where you went wrong or use the cursor back button to move the cursor back to the digit that needs correcting.
Just delete this one digit and replace it with a valid one.
You can also press escape to cancel the transaction.
You cannot use the mouse to move the cursor or to leave the field.