I remember attending a pretty large seminar with a shihan at a dojo where I went "incognito" -- sans hakama and in a white belt. A few people recognized me, but most didn't.
It was interesting to me that the people who seemingly gave me the most attitude were folks at around 2nd or 1st kyu level. Some seemed all too bored having to work with a white belt even to the point of one whom I remember who was watching other people training as they were uke. Yudansha didn't seem to mind and some seemed to pick up that I was capable in ukemi; I got paired with a 5th dan whom I knew (although I'm pretty sure she didn't know me) during jiyuwaza and she proceeded to wipe the mat with me (including some great koshinage).
So it goes.