Scorched Skeleton commendation count going up only 1 per firebomb/chest-explosion

I have been testing this for quite a while now and am confident to say that each throw of a firebomb, each explosion of the chest of rage, no matter how many skeletons are affected by it, will only give you one count.
I finished all the other commendations and am at just over 500/1000 for this one. I noticed this just in my last playsession, what leads me to think that this happens once the other commendations are finished and stopped counting. It seems to me that progress on this commendation was a lot faster while I still had to hit 3 skeletons at once. Therefore I believe I encountered a bug, but would like your input on it, maybe someone who still has to fight 3 skeletons at once would be willing to test how many of them count per throw of a firebomb.