Rails 3.1 Asset Pipeline: Precompiled MD5 Fingerprints don't match

I'm having a Rails 3.1 rc6 app on Heroku's cedar stack (ruby 1.9.2).

I precompile assets using rake assets:precompile RAILS_ENV=production locally on my development machine.

The problem is the generated开发者_如何转开发 md5 fingerprints in the precompiled filenames don't match the ones generated by the rails helpers (like asset_path) in production on Heroku.

Does anyone have a clue why this is? How can I fix it? I can't precompile on Heroku, as they have a read only filesystem.

Bit of a stab in the dark, but when I upgraded to rc6 today, this broke in an initializer:

if RAILS_ENV == 'production'   

and was fixed with this:

if Rails.env.production?

Don't know if that's got anything to do with it.