repond_to? bug, really strange

This is really strange:

User.send(:merge_joins, "one", "two")

=> ["one", "two"]

User.respond_to?(:merge_joins)

=> false

Am I missing something here? Shouldn't the respond_to return true?

By default respond_to returns false if a method is private (such as
merge_joins) but send ignores privateness and protectedness

Fred