Not actually a bug but..
I got the quest from Yukon and went to AI to get the beast..
the quest states "Travel to Abandoned Island into the snow covered mountains and slay the beast that Yukon calls The Abominable"..
I did that twice and the quest did not update .. deleted it - got it again - same result ..
As a dragon I flew to the top of the mountain .. it was only after running around for a while up there that I hit the trigger spot to update the quest - then it proceeded normally..
Can I suggest a change in the wording to something along the lines of :
"Travel to Abandoned Island into the snow covered mountains and find the lair / find the hiding place of the beast that Yukon calls The Abominable."
Else something to make it a little clearer that you are looking for a location not actually slaying him at this point.