Apparently, this piece is the composer's piano improvisations during a performance of Luigi Pirandello's play Six Characters in Search of an Author at the theater in Polička on August 29, 1929. The music was probably never notated, but there may be a connection to two eight-bar incipits currently archived at the Bohuslav Martinů Center in Polička, see H 181bis.
Harry Halbreich, Bohuslav Martinů: Werkverzeichnis und Biografie, Mainz: Schott Music, 2007, p. 223.