I'm resurrecting this thread because I have the same query. Periodically, I'll boot up the PC and there will be a flurry of HDD activity. Low and behold, Everything says "Scanning" in the status bar each time this happens. But it doesn't seem to happen for any particular reason.
Whatever is going on, I don't think it's supposed to be. It's as though Everything has lost it's DB and it making a new one. As David said, the indexing should only happen once, right? I really like Everything Search, so I'm keen to solve this.
If anyone doesn't like thread resurrections, tough