"Fail on certain moon phases" reminds me of a C++ bug I encountered while trying to set up the demo for PSIP (Digital TV Guide) destined for NAB in Las Vegas. We had programming schedules resembling excel spreadsheets and my job was just to create a good one for the demo. I would spend all night making one and sent it to my boss and each morning would get in trouble for sending in blank schedules and had no idea why. On one occasion I happened to be editing at 3am and noticed all of my edits rolling back one by one. It was actually viewable on the screen as if someone took control of excel and was rolling back each field. My immediate thought was I really need to get some sleep but later we found the auto-save feature inverted itself after 3am exactly and would go through each delta one by one rolling itself back as it had been edited. The bug was found in the calculation of the vernal equinox which moves from 3am to 9pm to 3pm. Since it was triggering the leap year code 6 hours of time would get rolled back edits and all! This was of course 2008 year of the digital transition from analog cable which happened to also be a leap year.
