When I choose a date on the calendar, then type a second date in that event (simply as a note to myself) the app changes the entire event to the date I have typed in only as a reminder!!
Ex: chose 2/7/19 from calendar, typed: pick up cake for so-n-so’s birthday today. (Party on 2/9). Without realizing it, your system had changed my 2/7 event date to 2/9! Sometimes it will even extend the date from (ex.) 2/7/19 through 2/9/19, making it a THREE DAY EVENT.