Walking between an instructor and a kamiza is a huge faux-pas.
You know, I seem to be the only one at my dojo who practices this. Although there are some who practice more formal etiquette than myself, this one escapes them.
It was the way I was taught at my first dojo. There are a few pretty strict Sempai at my current dojo, but I have never seen anyone practice this. And they seem confused when I do (at least to me, I'm not a mind reader). I have never gone into detail about why I do it though.