Namespaced object in the session?

I'm using Edge Rails. I'm storing a class called Hark::Session in the
session. When Rails reloads the session for the next request,
stale_session_check ends up calling load_missing_constant("Hark::Session").
I have two problems:

1. Why is it a missing constant? In application.rb, I require
'hark/session', and lib/hark/session.rb does in fact define the class.

2. Why isn't it found by load_missing_constant? It's in the right place,
given its name, and yet I end up with:

Session contains objects whose class definition isn't available.
Remember to require the classes for all objects kept in the session.
(Original exception: uninitialized constant Module::Hark::Session
[NameError])

Jay Levitt