ActiveRecord::SessionStore breaks with custom model

When using ActiveRecord::SessionStore for session management with a custom model class (set using ActiveRecord::SessionStore.session_class=), the custom model fails to work if it inherits from ActiveRecord::Base (which is the usual case).

The concrete problem seems to be caused by the fact that some class variables of ActiveRecord::Base are inexplicably set to nil sometime after the class is assigned to SessionStore.session_class. The two cases where I know for certain that this happens are Base.skip_time_zone_conversion_for_attributes and Base.default_scoping.

I have isolated the issue to how Rails handles application classes between requests in development environment, and I believe the process, in which things break is roughly this:

1. Server boots
2. Application classes are loaded
3. initializers/session_store.rb is loaded and a model class is assigned into ActiveRecord's class variable
4. Rails throws out application classes after a request is completed (because of config.cache_classes = false); meanwhile, ActiveRecord still maintains reference to a class that's no longer supposed to exist, and was crippled by the unloading mechanism. Somehow, in this stage, that model's class variables are set to nil for some reason.
5. Application classes are reloaded, but the new class objects are different from the one retained in ActiveRecord.

Based on my hypothesis, I devised a quick fix for this:

class ApplicationController < ActionController::Base before_filter {|c| ActiveRecord::SessionStore.session_class = UserSession}

...which seems to work. I'm not familiar with the unloading mechanism in Rails, and so I'm not sure how to fix this, but I would say it's relatively critical, since it basically makes the ActiveRecord store useless for all but the simplest cases.