Rails 3 - Custom Inflection Not Working?

I'm using Rails (3.0.3) and have the following code in
initializers/inflections.rb

ActiveSupport::Inflector.inflections do |inflect|
inflect.irregular('nursery', 'nurseries')
end

From the console I'm getting:

"nursery".pluralize => "nurseries"
"nurseries".singularize => "nurseries"

I should be getting:

"nurseries".singularize => "nursery"

Any ideas?