prepend_view_path not working

There's a view_paths accessor method. If you log view_paths does that
show your results as you expect them?

Well, it sounds like the code you should be looking at is in
ActionView, and depending on how fresh your version of Rails is, I'd
be looking in base.rb at the render_file method. Whenever something
like this stumps me, I use logger.debugs just like you are -- if you
want to go one more step, try ruby-debug and step through the render
sequence to find out exactly how your template is being located.

Sorry not to be of much help here.