is the model() method no longer necessary

I'm under the impression that the model() method is deprecated and that
all ar models should be loaded automatically. They aren't getting
loaded in some cases. For example, I'm using memcached for my session
store and it fails if I put one of my ar instances into a session
unless i use the model() method in application.rb for that ar class.
Actually it works fine in production mode, but fails in dev and test
mode.

I'm not sure if this is the way it should be or if it's a bug. Can
anyone clarify?