Delegator does not delegate protected methods
The Delegator of the "delegate" standard library has changed its behaviour since 2.0 because of the change in "respond_to?" concerning protected methods.
As of ruby 2.0, Delegator does not delegate protected methods any more.
In case this is indeed a bug, I will prepare a pull request on github fixing the issue.
On the other hand, if is intentional behaviour, something has to change in the documentation for "delegate" as well as Delegator#respond_to_missing? (at least the second argument's name). I can help with the code but I am not so confident in my documentation skills.