I found another issue: i created an event and i repeated it every 2 days from 4 to 8 of February. In this way i have 3 events on the calendar. If i delete the first (event on 4 of February) the repeated events disappear too. But if i leave the calendar and after i return to the calendar page i found the 2 events repeated (in my example events on 6 and 8 of February).
Another thing: the icon to delete the event on the calendar on front end (i suppose that is an X) is not visible.