My iPad reset its own passcode
I rarely passcode my iPad. A couple days ago, I did, using my debit card PIN, and the first time I tested unlocking it, it worked. After leaving it for an hour, I came back and the passcode didn't work. I tried every similar pattern until it locked up but honestly, it's my PIN, I use it dozens of times a week, and plus I tested it, and I am certain the code changed by itself. I am the only one who knows my PIN.
I have been forced to restore it, but it was very inconvenient because I was 500 miles from home (and my sync computer) when this happened, and since I use the device for work I had to change my travel plans.
Is this a thing that happens? I don't see a lot of people complaining about this.
iPad (3rd generation) Wi-Fi, iOS 5.1.1