A friend of mine had the same problem with USPS. I have had the same issue with FedEx, including them claiming that no-one was home twice when I was in fact home.
I happily pay the extra dollar or two for UPS. No BS, just my stuff getting delivered.
Check the parking lot/bike rack to make sure your bars aren't sitting on somebody else's ride. My experience with Postal workers tells me that they are more than stupid enough to 'liberate' something and then try to pass it off as their own.