I can't even get to this problem...my bend will shout doesn't appear to have any effect on Sahrotaar at all....there have been a few occasions where after about the fourth time I used it he just stopped and sat there. There were no options to mount him and he doesn't respond to attempts to initiate dialogue. But even getting to that point is difficult and takes forever because every time he hits you with his frost breath you lose all progress towards being able to shout again. This is getting really disappointing as I've played through the entire game twice now to get this point and it keeps happening...I don't even use any of the afforementioned mods either, with the exception of the unofficial dragonborn patch which I just now installed in an attempt to fix it...