Calendar Bug?

[dec.]

Out of natural curiosity I wanted to see when my 666th birthday is so I fast-forwarded in the calendar and saw that it's Friday, August 23rd, 2639. But when I look at the black marked date above the calendar entry, it shows Friday, August 22nd! So I checked other dates and it seems that this happens all the way through from Sunday, March 14th on. If you see the second screen in the image, there are two March 14th displayed, one Sunday, one Monday.
Obviously iOS7 won't be relevant in 2060, but I'm still wondering how this happened? Or am I dating it wrong?

 

[dictoresno]

some people reported a birthday calendar bug in the betas where it reported birthdays as being one day off. i have numerous birthdays saved in my phone and dont have this issue though.