This doesn't necessarily have to be something nefarious, nor necessarily even something tying the date to auto-focus. It could easily have something to do with doing something on a timer, or measuring how long it's been since you did something last, etc. If you're performing some activity repeatedly, on a time-based interval, or only if it's been a certain time since you did it last, and you're handling dates/times in an incorrect manner, then things that should be done could end up not being done, or things could end up being done too seldom or too often.
I worked on a telecomm product once that, during testing, suddenly dropped all its circuits one day. Turned out that this was repeatable, and would always do the same thing on that date, and also on a series of future dates separated by some consistent interval.
-harry
