Why are my ActiveRecord class instance variables disappearing after the first request in development mode?

I have a class instance variable on one of my AR classes. I set its value at boot with an initializer and, after that, never touch it again except to read from it. In development mode, this value disappears after the first request to the web server. However, when running tests, using the console or running the production server this does not happen.I have a class instance variable on one of my A