I received two birthday reminders in my email today for the same user. They were sent at the following times:
Sun, 28 Oct 2001 01:11:42 -0700 (PDT)
Sun, 28 Oct 2001 01:13:19 -0800 (PST)
My guess is that the birthday reminders are set to automatically be sent around 1:00am. Since daylight savings time occurred last night, the server clocks probably set themselves back an hour, from 2am to 1am. So I think the birthday reminders were sent out twice.
If this is the case, my suggestion is to put in a check for the occurrence of daylight savings time clock adjustments before sending out the birthday reminders. Thus, the birthday reminders wouldn't be sent out twice.
Like I said, I'm not sure if this was an actual "bug" or if it was just some random odd coincidence. Others out there will certainly be more knowledgeable than I.