I've been having the same issue. Never happened when Windows 8 was installed.
I have had 8.1 installed since it's availability and has only started this restarting over the past month. It happens when removing and attaching my type cover - also version one.
I factory restored my device a couple of days ago and I'm still having the issue.
I was speaking to an MS representative today and he has logged it and said people should start investigating it very soon. Hopefully a couple of weeks for them to find a resolution.
I'm contemplating taking it back to John Lewis and seeing if they will replace it with a Surface Pro 2 (as this is my second replacement, however for a different reason). So if I was to take it back it would be my third.
I'm experimenting by not using the type cover and using my wedge Bluetooth keyboard and seeing if the issue happens. I don't think it will. I know there was an system update applied on the 10th of this month - I'm wondering if it's related to the firmware upgrade. Really don't know - just wish it wouldn't do this as it's irritating especially if you are doing something productive.
It's very strange that there is nothing helpful in the event viewer.
Anyway, I will update you if I hear anything back from Microsoft.