(a) Except as provided in subsection (b), the plaintiff has the burden of proof on all issues of fact raised in connection with a preliminary objection.
(b) If in support of a preliminary objection a defendant alleges fraud, corruption, bad faith, or gross abuse of discretion on the part of the plaintiff or any of its officers, agents, or employees, the defendant has the burden of proving by clear and convincing evidence the facts relating to that particular allegation.