jurisdiction in issue

[A] question [of jurisdiction] is in issue only when the District Court's power to hear and determine the cause as defined and limited by the Constitution or statutes of the United States is in controversy, and where a District Court is vested with jurisdiction of a cause, as where diversity of citizenship exists, and the matter in controversy is of the requisite value, the question whether it has the power to afford the plaintiff a particular remedy does not present a jurisdictional issue.