Renamed my save folder and started fresh. Created "Dude Bro" and tried for baby the first single woman he ran into. She called 3 days later to say she had twins.
She was dark-skinned and I've noticed the babies seem to be somewhat inconsistent when they are twins. With my other guy, he has light tanned skin, black hair, and green eyes. One of the mothers has very dark skin, black hair, and brown eyes. Her twins with him were as pale as the palette goes and one had red hair and blue eyes; while the other had pale skin, black hair, and green eyes.
So it doesn't appear to be a cache issue.
EDIT:
I got a response to this same topic on another forum and others have been reporting the same issue. One said her Sim's kids have all grown, married, and had babies and each of the 3 kids all had twins when they gave birth while inactive.