I just posted a reply to someone in Outlook 2007. Then, briefly my list of Sent Items looked like this:
It seems that even though I sent an email at what it knew was 00:00 which can (should) only ever be today something hadn't updated the date for the comparison of now and the date the messages was sent.
This is one of those issues which just looks foolish when you see it but very few people will ever see it. It's also something that'd likely be very hard to test and unless you knew this sort of issue could occur you'd be very unlikley to look or test for it.
I guess this is merely just an observation. It's not like this would be easy particularly or worthwhile to fix. I merely note this here so you might think about and avoid similar issues in any code you write.