I have the same bug with the pocket plane ability. Do you want me to upload baldurs25.bcs and my last savegame?
 
Also: After killing Sendai and Abizagail and upon returning to Amkethran, Balthazar is not on his throne. He is nowhere to be found.
C:CreateCreature("Balth") spawned him in his throne room. After that the conversation can be initiated.