It has never happened to me - yet. From what I've read in the threads discussing this the common factor is that the game is off and the player has opened the game to find an over-50 nursing. Just recently I had a 44-year-old male set to parenting as I was trying to bring him up to Scholar. He was an adept and had happily been running around kissing all the girls he could. Suddenly I noticed he wasn't "performing" as before. he was carrying out any action other than the one I wanted him to do.
I then realised that he'd perhaps been a little too enthusiastic and had impregnated every female between 18 and 50. I decided to use "speed-kissing" and eventually brought him up to a Master Parent and thus a Scholar. The Elderly Scholar who was his partner in the speed-kissing must have been kissed a couple of hundred times but didn't have a baby. If, however, I'd turned the game off for a while, she might well have done...
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To err is human; to arr is pirate.