Hi @Zachary Whyte,
thanks for your answer. I no longer have earlier save files, since I moved on in the game and did not make a backup of an earlier date.
Nevertheless, I tried exactly that. When I used the save game from a weak earlier, the result was the same. That is why I did not bother keeping another save file.
My only idea besides a bug would be, that he was not interested in a transfer. Actually, I know that he was not interested in a transfer because he rejected a contract after I bid more money (this offer was accepted).
But I would assume that contract offers and transfer offers would be handled seperately, so I would not expect a connection between optional future fees and contract talks.