So, if I continuously want to add and remove functions within one shell (running hypothetically forever), do I have to 'manually' delete those empty left-behind files? --- that is, not only use
fn name_that_I _don't_need
but also
rm /env/'fn#name_that_I _don't_need' ?

No.

Well... that's an answer, but not very constructive indeed. When do those files dissapear?
R.