<=> comparison operator method undefined in AR class

I had the same behavior with acts_as_commentable. Acts_as_commentable belongs_to :user, and I could not access any methods I had defined in User after the first request. I solved it (thought I don't know why) by moving comment.rb from /vendor/acts_as_commentable/lib to /app/models. I don't know if this is related to your problem, but the behavior sounds awful similar.

Aryk Grosz wrote: