I've never had this happen in my game as far as I know. I have been seeing some odd behaviors lately though myself. The last family I played the female sim would randomly keep yelling at her husband who she had full relationship bars with. She had no negative sentiments towards him or him towards her, he had no indiscretions with other sims and neither one had any bad or mean traits. It kept bringing their relationship down each time it would happen and their relationship was always romantic and loving in the past until the last update.