The only time I've ever had this problem is because USPS in my area (Allen, TX at the time) was so inept it was impossible to find out when I was going to get things. They would scan packages when they loaded the truck as "delivered" when they clearly were not.
I actually had USPS as a customer at the time and told their top management what was happening. Never found out if they did anything. Don't live there anymore so I don't really care.
The worst thing they did was leave outgoing mail in the mailbox and put the incoming mail on top. Apparently my carrier missed the "little red flag" class.