If I create an event and set the start and end dates as the same day, and set a start time with no end time, when I save the event, it changes the end date to one day later. This only happens when I choose to have the event recur Monthly By Day in Week.
Maybe you can attach a screenshot of the settings which you entered when create that new event? Base on the data you provide, we will try to re-procedure the issue and in case it's valid, we will fix it