Not able to loot boss when getting run through instance

[Gryffon]

Its been around for awhile that if you dont tag the boss in an instance as the person getting run through an instance you might not get the loot. However, recently it seems to have gotten to the point where you NEED to tag the boss in order to get the loot. Is anyone else seeing this as well?

I have been running my 20 through some instances on my alternate account and have noticed that some bosses, seemingly randomly I am unable to loot the boss after I kill it.