The map actually was not corrupted; the server settings set the Victory Provinces. The map itself has 1 Victory Province set, so the first will be there; the rest will be set randomly, I guess. But now there should be only 1 VP Province.
Mr. Falcon is correct. By default Dominions seems to add a few VPs. But I've now found the switch to set the number of added VPs, so this time I set it to zero.
It was quite lucky actually that the mistake was visible, since I completely forgot to set the VP settings the first/second time. Now it is correctly set to accumulate VPs each summer, with 3 VPs being needed for victory. Of course most probably the VPs will be acquired by more than one member of a team, so the victory will have to be determined manually by the players.