You could rule out corruption by deleting your ports tree and and redownloading it using
portsnap(8). If you still have the issue, corruption is out of the question. If you do not, you still would not know, but you could go about your business while retracing your steps to find administrative mistakes and waiting for further corruption.
EDIT: After reading your post again, it appears that you have already tried fetching a fresh tree. A full deletion and redownload could not hurt, though.