There was a patch note on the beta about this quest being fixed… But it does not currently work on the live servers, I tried to attempt it a few times and the mount just randomly “breaks” despite being nowhere near the icebergs.
I think it is dismounting as soon as you enter The Frozen Sea zone and leaving Grizzly Hills zone. I tried to find a route through the water that is 100% Grizzly Hills but have been unsuccessful.
I just posted on the other thread my thoughts on why it may have worked after the 6th try if you want to read it there. I guess I can’t repost here for it being too similar?
I tried this quest six times today and FINALLY I didn’t get dismounted. Try to go down the path quickly on the left side where the rocks are. Other than that, this time I had dismissed my pet as a hunter and turned off aspect so I’m thinking 1 of those 3 reasons was why it worked this time. If you’re another class and the path I mentioned didn’t work, try turning off all your buffs, dismiss any pets (hunter, warlock, DK). Only thoughts I can give, hopefully it works for you while we wait for blizzard to fix this bug!
I’m surprised this quest didn’t get the fruit treatment that the art work got.