I'm with the same bug, but with the Kerghits. I defeated all of them, captured all their casttles and cities, but the war still remain after almost 50 days. I'm searching for their troops with cheats, killed 2 that I found, but the war still remain.
Has anyone reported this as a bug at http://bugs.taleworlds.com/ ?
Edit: Yes, there is: http://bugs.taleworlds.com/edit_bug.aspx?id=3132