The more senior a staff member is, the less likely they are to look through or ignore a person in uniform.
This was particularly shocking for me to experience first-hand, as I went from "doctor" dress one Friday to "uniformed staff" dress on the very next Monday. Suddenly I went from a person who you would look in the eye and smile at on the way past, to being part of the wallpaper.
One thing that I have noticed is that the more senior staff members will still talk to me (without knowing I'm a medical student, although that shouldn't matter) but many of the interns and junior registrars will look straight through me, and one has even rolled her eyes when I show up to do a mobile x-ray. Seriously. She asked me to be there. I was pleasant and professional. She rolled her eyes. Somebody clearly has issues.
I know that this is a generalisation, and there are many junior staff who will talk to everybody they work with. It is just something that I really noticed between one "work" day and the next.