Had a
similar problem a while back, specifically with just the Backup task. At the time, I think we were trying to include Imported Items which was causing the backup to run through midnight into the next day. AC would get confused (this is according to AC Tech Support) because the backup was starting late at night and not finishing until the next day. To fix it we moved the backup to start at 12:01 AM.
FFW to today, running 9.0, we haven't had that issue that I am aware of. To double check, even the time stamps on the backup files for the past 30 days have the same time.