Why do some champion / elite packs give a double stack of Nephalem Valor?

Solution 1:

As suggested in this post, there currently seems to be a bug when killing several monsters of the same pack at the same time.

What happens is that the last two monsters of the champion pack dies at the exact same time, triggering the Nephalem Valor stack 'gain' twice.

The above post seems to point that killing more monsters of an champion pack could give you more stacks of the buff.

Note that this can only happen on champion packs, not rare mobs, as only champion packs allow different monsters to trigger the Nephalem Valor 'gain'.

Even if the post has no answers from Blizzard, I guess this will be considered as a bug and fixed somewhere in the future.

Edit : The bug has been fixed with a hotfix on July, 3rd 2012.