Hi, Jamie -- I know I already emailed you about this, but a little more info might help.
I've had this happen a few times over the past week, and it seems to be when there's a delay between starting the new profile and ultimately clicking to save it. For example, when I'm going through multiple potential duplicates or get interrupted by something else.
Now that Kenneth & Kitty mention it, I do think it was happening more often when I was adding a sibling, but I didn't really pay attention to that. I will going forward, though.