At a recent conference, I encountered a senior professor in my field -- someone I had first met many years ago when I was an undergraduate and he was a professor at a university not far from the college I attended. He and my undergrad advisor were sort of colleagues, so this professor sometimes came into contact with us undergrads. I did not particularly like him at the time because he seemed obnoxious. Typically, when visiting one of our seminar classes or playing a role in an undergraduate research project, he wouldn't speak directly to us undergrads, but only to his colleague, our professor.
Over the years, I have had various indirect professional interaction with him. We haven't collaborated, but our research interests overlap enough that we have interacted to some extent. At this recent conference, we spent a lot of time talking about mutual research interests, and he was genuinely interested in some of my ideas. We had a very collegial interaction, although I don't think I will ever be entirely comfortable around him.
I don't hold a grudge against him because he was rather rude and dismissive of me when I was a mere student, but at the same time I am aware that he is the kind of person who treats people with varying levels of respect depending on their academic status. He was a big professor at a big research university, and he just didn't see undergrads.
But he sees me now, so I suppose that is a semi-good thing in that he is capable of evolving in his interactions with individuals over time. That is, he doesn't still see me as an undergrad just because that's what I was when we first met.
I was thinking about this general issue recently because someone asked me whether it is a good thing or a bad thing to be hired as a professor at the same institution where you were formerly a student (undergrad or grad): would your former professors/now colleagues always see you as a student, or would they see you as a peer?
I have no direct experience with this, so those in this situation as ex-students-turned-faculty or as faculty who are now colleagues in the same department with former students of that department can better address this issue.
Years ago, the chair of my former grad department informally asked me if I'd consider a faculty position there. We didn't go too far with this exploratory discussion, but it made me wonder what it would be like to be a professor in the department where I had been a student. Would the faculty who were there when I was a student truly treat me as a colleague, or would they remember me always as a student?
From my indirect experience with colleagues and friends in those situations, I don't get the sense that the once-a-student/always-a-student syndrome is common. If a former student of a department is hired as a professor in that department, it may indicate a high level of respect for that former student.
A cynical alternative hypothesis is that hiring former students involves cronyism and/or inbreeding.
Most likely, the answer varies quite a lot depending on the institution and department culture, but I'd be interested to see a discussion of examples and opinions.