The Days Of the Week Have Changed!

I've been using Sky Safari for sometime now. But today, something strange has just happened. I always look at what astrinomical events took place in the distant past. I write down both the date and day of the week the event took place. But today, I noticed that for some strange reason, all the dates in the B.C. years have changed! They no longer fall on the same day of the week as they always have been! I don't understand why this has happened! Has anyone else had this same problem? I don't like this because it now makes me not trust Sky Safari as a reliable astronomical software program. I really hope this was just a program malfunction. This has never happened before.