I'm in the soldier's mess hall and I kill that's there. The save point glows, but I cannot save. Farah keeps shooting arrows at non-exsitant targerts. Nothing happens. So I climb up the debris and reach the alcove where I can get a sandtank refill. Then suddenly new soldiers appear on the ground and attack farah. I can't get down anymore without plummeting to my death and the soldiers kill Farah if I don't rescue her. If I run to the drawbridge, the soldiers also kill Farah. This is surely a bug in the game. How do I get out of this?

I'd suggest restarting the level...that never happened to me....

That happened to me on a different level. walk around where farah is shooting at and if the prince starts to crouch as is to fight slash with your sword, they will either die or appear, also trying doing flip attacks over the invisble enemy.