nil object error when speccing a helper method that calls content_for

I'm in the process of upgrading a production app to Rails3 and ran into an odd error while updating my specs for rspec2. I have a helper method that uses content_for, and when running the spec for it, I get an error like this:

Failures:
  1) page_title should not fail
     Failure/Error: page_title('A', 'B', 'C')
     You have a nil object when you didn't expect it!
     You might have expected an instance of ActiveRecord::Base.
     The error occurred while evaluating nil.[]
     # /Users/tsigo/.rvm/gems/ree-1.8.7-2010.02@rails3/gems/actionpack-3.0.0/lib/action_view/helpers/capture_helper.rb:137:in `content_for'
     # ./app/helpers/application_helper.rb:3:in `page_title'
     # ./spec/helpers/application_helper_spec.rb:7
     # /Users/tsigo/.rvm/gems/ree-1.8.7-2010.02@rails3/gems/activesupport-3.0.0/lib/active_support/dependencies.rb:239:in `inject'

• rails 3.0.0 final
• rspec and rspec-rails 2.0.0.beta.20

It seems this is caused by ActionView::Base not being initialized during the spec process, so @_content_for never gets its initial Hash value and throws the nil error when trying to append to it.

I'm not sure if this is actually a Rails bug or something I'm doing wrong inside the spec. I've created an example Rails app that duplicates the behavior at http://github.com/tsigo/content_for_bug