Kardur Doomscourge and Propaganda in multiplayer

If an opponent (A) plays Propaganda and then I (B) play Kardur Doomscourge in a multiplayer format (we were playing commander), you (C) are forced to attack even if you are completely tapped out. This caused a softlock as player C was forced to attack but there were only three of us and that player had no other players to attack. We did not attempt to rollback, player C simply conceded.