In this new post on his blog today, Derick Rethans points out something that might confuse some when it comes to date/time handling - a few seconds of "lag".
"strftime usually returns a string from the number of seconds since 1 jan 1970. Now, it lags and returns a string representing 23 seconds too late."
If you know what's going on though, it isn't really that weird.
Bug report #35958 must have the most obscure one ever:
He talks about the leap seconds that have been added to keep things straight, and how that's affecting PHP's built-in date/time functionality. He also shows an example of how you can get the "more correct" time versus the normal output...