by Davo Smith.
Just to clarify - this has always been my understanding of why you can't submit assignments when you have done 'switch role to'. It may not have been the exact reason why it was so (but it makes sense to me).
My preferred solution, especially when I wanted to demonstrate to students how to submit work, was simply to assign myself the role of 'student' in addition to 'editing teacher', at the course level. That way I could submit work and have it show up on the grading page.