[iMore Question]

I try to add event from past and it disappears after pressing done

[Bigeric23]

Go to Settings > Mail, Contacts, Calendars > Sync and check your settings.

[Just_Me_D]

I try to add event from past and it disappears after pressing done

What do you mean you tried to "add an event from past"? Are you trying to add a new date to a past event? If so, just change the date & time. It will indeed disappear from the screen until you change over to that specific date in your calendar app.