In my view, roles are things that we 'buy into' or 'project onto' others. They are not really Real in any deeper sense. So, if I decide someone is my teacher and learn great things from them, it doesn't matter if they are not trying to teach or thinking of themselves as teaching or taking responsibility. Similarly, when I decide that I enjoy teaching or that I learn from it, I do this primarily for myself. Whether or not anyone (except me) actually learns anything is almost beside the point. I may learn quite a bit by deciding that I am a teacher and taking lots of responsibility for the progress of a whole bunch of people, and if I did then that's important whether or not those people even knew that I was 'teaching' them.
The really interesting thing happens when people approach these roles with expectations. This can happen on both sides: teachers who feel their students are not living up to responsibilities and students who feel their teacher should be offering more. The reason this is interesting is that it creates a 'situation of conflict' that is somewhere between being 'in the dojo' and being 'out in real life.' It is a real opportunity to harmonize and learn to find creative ways of approaching the situation, without giving up what you see as your own needs.
One of my teachers was very niggardly with feedback and, at the same time, reticent about discussing his own aikido. I often felt at sea. One thing I learned was how to deal better with my own curiosity and need to know. Another thing I learned was how to find the right questions that would provoke the answers I felt I needed. Both of these were valuable lessons, although the first threw the responsibility back on me as the student and the second was about finding a way to get him to perform the role I felt he should.