Presenting what the 7th U.S. Circuit Court of Appeals called a “knotty problem” about supplemental jurisdiction in a case about allegedly leaky windows manufactured by a company referred to as Ply Gem, a handful of unhappy homeowners joined Prolite Building Supply in a state court lawsuit that was removed to federal court based on the diverse citizenship of Prolite and Ply Gem.Prolite sued Ply Gem for allegedly breaching a service agreement. Ply Gem and an affiliated company (Great Lakes Window) countered by …