The problem is that:

  sub Create_hashref{
    {@_};
  };
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is less than unambiguous... It might look like an anonymous hash constructor to you, but it's actually a BLOCK containing the rather trivial expression @_, whose value is the length of the @_ array. This:

  sub Create_hashref{
    return {@_};
  };
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takes a different view. As does:

  sub Create_hashref{
    +{@_};
  };
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This is discussed in Making References -- see paragraph 3.