Muh - Ahh understood. I didn't see where you mentioned that, so I thought it was a bug.
Personally, I'm against this change and think the official behavior is better. A lot of MVPs have mechanics to use skills like earthquake or TP when they get to low HP thresholds, so the player will either die or the mvp will tp away. As a result, in a contested scenario, the players who get to it after these HP thresholds are the ones who are rewarded rather than the players who do the most damage.
I've experienced it both ways: losing an mvp after getting it low and winning an mvp after the contester got it low. In both scenarios, I felt that the person who did the most damage deserved to receive the rewards. I think the change makes sense for normal mobs, but the official behavior makes more sense for mvps.
Not sure what behavior you mean when you say "chicken out," since it doesn't seem like a common case where a player will do more than 50% of the HP and decide to stop killing the mvp.