I'm not sure that I've ever tried this before, but this was driving me nuts. Everytime id try to create an event, the event would disappear. I couldn't figure out the issue, but I think I narrowed it down... If you create an event and just put someone's name in the "who" field, without actually selecting a contact or using an email, and then save the event, the event will delete/disappear. I thought I was going nuts, although I don't see the need to delete the event.