Talk about a fine distinction. For me, "professor" means someone who teaches at a university. I don't care what the official title is - if you're getting paid to teach in a classroom at an institution of higher education, you're a professor. Now U Chicago is clarifying things:
From 1992 until his election to the U.S. Senate in 2004, Barack Obama served as a professor in the Law School. He was a Lecturer from 1992 to 1996. He was a Senior Lecturer from 1996 to 2004, during which time he taught three courses per year. Senior Lecturers are considered to be members of the Law School faculty and are regarded as professors, although not full-time or tenure-track.
So hopefully that puts an end to that little escapade.