I had an adopted girl disappear when she was 17..

It is kinda like Narnia, but she came back an adult. I passed the house to her..

I just had a strange thing happen. I had just handed the house over to a female child and she was looking around when a proposal came through. I am trying to get same career trophy so I hit Alt-F4 rather than Reject. When I restarted the game, the unwanted suitor is there as her husband. The strange thing is he does not appear in the Family Tree. They have had 2 kids so far and it looks like she is a single mom on the family screen. Anyone else had this? Will he ever show up in the family tree?

I won't do that again.

Yes, that can happen if the game crashes (which is what, in essence, happens when you use Alt-F4). This thread details a very similar situation.