The claimants allege the works were left with Grosz's dealer Alfred Flechtheim when the artist was forced to leave Germany in 1933. The New York Times summarizes the plaintiff's version of events
Charlotte Weidler, an art dealer and curator for the Carnegie Institute in Pittsburgh, said that she had inherited “Portrait of the Poet Max Herrmann-Neisse” from Flechtheim and that she gave it to Curt Valentin, a German dealer in Manhattan, to sell to the Museum of Modern Art in 1952. The museum bought “Republican Automatons” from a Toronto collector in 1946 and was given “Self-Portrait With Model” in 1954.
Back in 2006 the Met declined to borrow the work Portrait of the Poet Max Herrmann-Neisse due to the potential lawsuit.