@sozobe,
I think it's stress, too. I talked to Mike about it once. He'd been with the P.O. a good while and had tons of vacation time, plus a generous amount of sick days. I mentioned to him one day how much we missed him when he went on vacation -- it was really noticeable lol. He told me how much harder it is for subs, that they have a million things to do in the morning and limited time to do it. It was a real eye-opener into their daily routine.
Our new guy subbed for Mike for a few months before he got our route as a regular schedule. Whenever we'd get our mail after dark, we'd say, "Mike's on vacation again" lol. He was the best, though. Always had a smile and something nice to say if I was out front when he came by. Things will ease up for the new guy...just takes time.