To my pleasant surprise I noticed that gnubg now contains a PartyGammon import function :-) Only when I imported a match I noticed an error: The first game my opponent won a point, the score then was 0-1 to 3. The second game I won a point. However, gnubg put the score on 1-2 to 3 then.
I attached the game history I was talking about (changed the player's names to player1 (opponent) and player2 (me))