I (male) publish with prof. x (female). We have also taught joint seminars, and given quite a few joint talks. On at least four occasions (including one formal solicitation to apply for a job) people have assumed we are married. (It would be remarkably easy to determine that we are not; in fact that we are both married to other people. There is no evidence beyond the joint work to suggest that we ever had any relationship beyond the professional, which indeed we have not.) None of this had sexist intent, indeed was in some ways friendly and generous (offering to create a second position). But we all need to think about the climate we create for students or junior faculty who are considering joint work if they get the idea that the default assumption among the community is that a man and a woman working together must be having sex.