I have noticed a big Increase in this. My sims husband took it upon himself to flirt with his father in law in front of his mother in law and his new bride. The father in law accepted it. They never had a romantic relationship before hand. Never. My gay sim Abby keeps getting texts from Paulo and one other guy talking about how opposite attracts and how they should go on a date and see if things get spicy. Abby lives with her girlfriend. She has never flirted with these men.
I assume its a bug.