Family tree glitch happening again?

Is anyone else experiencing the family tree bug glitch? Or is it just me? 

My married couple are parents of 11 (She has given birth to all of them in game.). They are also grandparents of 13. They were unable to woohoo in game suddenly. I happened to look at the family tree, and saw they show as brother and sister... Their children have been divided between them - Some are hers, while the others show as her nieces/nephews. I tried to cheat them back to normal but the game keeps changing their relationship. I rolled back to a previous save but they are brother and sister - even though she is pregnant - Weird.  This is a new save after the previous save changed them to father and daughter who shared their kids! 

I am starting a new save with a newly created family to see if it happens again. But just  checking whether it's just me having this issue again?