It's happening in my game and seems to be both social bunny and broken relationships or sexual orientation. I have boarding school or communal teen lots and those who live together all have romance meters regardless of sexual orientation. In fact if I go to CAS it will have changed from what I set the orientation to into interested in both genders.
If the non played sims send flirty anything through social bunny it starts a romance with my Sim. My teens are constantly building unwanted romance meters.
