I just entered this ticket.
It turns out that in an ActiveRecord model like this
Model << ActiveRecord::Base
The method public_method will be private because named scope overrides Ruby’s public method! Also this can cause additionally hard to debug failures in metaprogramming, I discovered this when the RSpec stub! method blew up when it used class_eval to generate a stub method which apparently caused public to be called internally by Ruby, at which time the named_scope generated method failed.
See the ticket for details.
I’m not sure what the fix should be, but I think that named_scope should not cause public/private, and the like to be clobbered.