We have just released an update to the Steam client that renames the MasterServers.vdf file to MasterServer2.vdf. This was to ensure all players refresh the list of Masters. Once you receive the update, your Client will automatically retrieve and save the master information in this new file.
This probably means that Setti's MasterServers.vdf must be also renamed to MasterServers2.vdf.
Can somebody test and confirm that the new masterservers2.vdf works with Setti? It should be as simple as renaming the file.