Apple Calendar not accepting event on first time entry

Hello, I use the Apple Calendar to schedule my upcoming events. Version 7.0 (1841.1) Lately, when I attempt to enter a new event, Calendar does not accept it on the first entry. I input my information which might include the type of calendar, The name of the event, the location, the date and time, and a few alerts as well as a note. I either push return or select outside the box to finish it. It immediately returns to the initial time without any of the information I just entered. I will then immediately input the exact same information and press return and this time, it accepts it. Anyone have any idea why this is happening and how to prevent it from happening? Thanks.