This was (mostly) fixedimplemented in March 2016. When the target question is unanswered, a different notice from the one you quote is now shown:
This question was marked as an exact duplicate of an existing question.
Note that until May 2018, this suffered from a bug, in which it checked to see if the closed duplicate question had no answers, instead of the target, when deciding if this notice or the other one should be shown. However, it now properly checks the target question and changes the notice as appropriate.