professors getting with students

wouldn't that be a huge no-no?!
It happens twice in this movie - both involving Patricia Arquette, as a student and as the professor (which only occurred to me as I was looking at the thread about their step-siblings - I wonder if that was deliberate mirroring from Linklater to show the pattern repeating?).
Anyway, I get that they're adults, but surely it would be inappropriate to not at least wait until the person has graduated or no longer their professor/student before getting involved romantically. In fact, if the professor is the one doing the pursuing, it could be perceived as an abuse of their position.
Or does it happen all the time and I'm just being naive here?